I'm not sure who needs to understand this most: kinksters who discovered BDSM through poorly written fiction or unrealistic porn, non-kinksters who only see a momentary glimpse into a relationship, or well-meaning people (kinky or vanilla) who only see the world through the prism of their own reality. But I'm going to break this down for you, whoever you might be, and whatever your reality is.
Consent always comes first.
Nothing that happens between a Dominant and a submissive should ever happen without full communication and negotiation followed by consent. Nothing. Not the first "Sir" or "Mistress," not the first time on your knees, not the first, second, or millionth sexual act.
Consent is earned by the Dominant and given by the submissive in every interaction. Always.
There are as many variations of Dominance and submission (D/s) relationship types as there are people. Master and slave (M/s) is going to look vastly different from Daddy Dom and little (DD/lg). The way you define your relationship: M/s or D/s or whatever; 24/7 to play; sexual or not sexual - all of that is unique to you and your partner(s). One thing is not. Say it with me, y'all: consent is a requirement.
I believe fully and completely in the use of safewords. The easiest way to stop an activity or an event is a safeword. Yes, it's most often found during a BDSM scene or some sort of sexual play, but a safeword is the removal of your consent from what's happening in the moment. While I find that most healthy D/s relationships allow for easy communication (in a respectful manner) for concerns and issues that arise, when all else fails, a safeword is there to stop any specific act you no longer consent to. And I think a Dominant should be just as free to use it as a submissive.
A caveat: I don't support using a safeword to get out of doing something you don't like. It's there to be used when you perceive a danger or threat to your mind or body. A safeword is not a catch-all for anything you don't like. Abuse of a safeword by a submissive means that there are much bigger issues in your relationship than disliking an activity. You need to deal with those issues through open and honest communication.
Okay, now that I've cleared that up - for anyone who might have been confused - let's move on.
Being submissive doesn't mean being a doormat.
As a submissive, I am willing to do many things for my Dominant. You have to realize that we live this 24/7. There is no break for us. There is, however, an ebb and flow. When one of us is sick, for instance, there is no face-fucking, on-your-knees-girl, spankings with floggers kind of play. But he is always Daddy, and I am always babygirl.
In our relationship, I make his breakfast, pack his lunch, prepare his coffee...and I'm sexually available, show deference to him in many things (nearly all), and consult him on major life decisions. I kneel twice a day (minimum) in front of him. I do as he tells me - both in the vanilla and the kinky moments of our lives.
That's how our relationship works. Even when I can't call him "Daddy" (how we address each other depends on who's around), I always show him respect. Even in my teasing, silly, babygirl moments, there is always respect. Those few moments when I go too far and forget myself, there are consequences - dealt at an appropriate time.
Someone might be thinking that I do everything and I have to show deference and you might mistakenly believe this makes me a doormat. What does my Dominant do for me? What do I get out of it? Why would I do this?
First of all, I don't bow down to anyone and everyone. I show respect to all who show it to me. My Dominant spent a long, loooooooooong time earning my respect and trust. He learned my likes, dislikes, preferences, moods, emotions, history, and anything else I was able and willing to share. I discovered that he is a man of honor, a man worthy of my submission. For him - and him alone - do I cede control. When we're in a group of Doms and subs, I address everyone with the same respect, the only difference is that I may use a specific title for a Dominant or refrain of touching (hugging, shaking hands, etc.) unless given the go-ahead by my own Dominant.
For him, I would defer to someone else, but only as part of my submission to him. He tells me to do something - as long as I don't find it horrible, objectionable, and outside of my limits - and I do it. The difference between him and some asshole is that prior to any demand, there will have been a discussion and if I'm uncomfortable in any way, I can say so. We can discuss it. I don't just lay down and wait for him to walk all over me. I am an active participant in my submission.
What do I get from it? Freedom, the luxury of a quiet mind free from a million worries, and a sexual, mental, emotional, and physical pleasure unlike anything I've ever known.
Being Dominant doesn't make someone a tyrant.
By mutual consent and agreement, Daddy is in charge. When I'm unsure of how he would want a situation handled or if I should make the decision on my own, I defer to him. Sometimes that comes in the form of, "Let me talk to Mr. John first" (when I'm addressing my children) and sometimes it's as "Give me a day or two to discuss this with my partner and I'll get back to you."
We've been together long enough - and we talk all the time - so I don't need to use these tricks often. I know what the answer is, and I know him well enough to know how he would respond in most situations. There are also situations that are completely within my domain. How much money is appropriate to spend on something. Groceries to buy. Work to be done. How I manage my day. But again, that's our relationship dynamic. A M/s relationship often looks completely different in terms of control and decision-making.
When he wants me to do something a specific way, he tells me. If I don't agree or am unclear, I discuss it with him. I ask questions. I respectfully make my point. In the end, I defer to his decision. But he always listens to me. And often, if I make a good point or show him another way of looking at a situation, he takes my advice. (For the record, my favorite words to hear from him are, "You are/were right, Babygirl.")
Every decision he makes (a huge responsibility, by the way) is with our entire family in mind. If he made selfish decisions, we wouldn't be together. I grant him control because I trust him to use it wisely, to think of our family's best interests - not just his own.
Do doormat submissives - those who do anything and everything their Dominant requires without a single thought to their own well-being, likes, dislikes, etc. and who forgive a Dominant who neglects consent - exist? Of course they do. I worry for them. Their issues are bigger than a run-in with a bad Dominant (as dangerous to their health and well-being as that can be).
Do tyrant, asshole Dominants - the ones who ignore consent and safewords, thinking of no one but themselves and their own pleasure - exist? Yes, and those of us in the BDSM lifestyle don't consider them "Dominants" but simply abusers who probably belong in jail. They are what we fight against every time we talk about BDSM with someone new.
I don't ask that the world understand my relationship. I share so much of it in hopes that more people will relate and that I might reach a confused kinkster or two and help them grow and learn. But you don't have to understand me or my need for submission or his for Dominance. What I ask is the same thing I grant the world around me: respect. The key to everything in life is respect. And if you ever find yourself confused about why someone submits, gives up control, and let's another person lead, realize that the center of it all is respect. A good Dominant earns it, and a healthy partnership exudes it.
Just a side note: if you notice, when I discuss D/s, I don't always focus on the sex. D/s is how you relate within a relationship: one person gives control, the other person accepts responsibility for being in control. BDSM is the sexual act, practice, or preference. They often go hand-in-hand with a D/s relationship, but not always. You can be D/s and have all the vanilla sex you want (hopefully it's good sex, no matter the flavor) or not have a sexual relationship at all. You can be into BDSM and not relate as a Dominant or submissive. What matters is consent, communication, trust, honesty, and yes, respect.