Step one: Communication. You need to speak to her frankly and openly about your desires. Open a dialogue, show her some fiction with your fantasies in it, get her to view sites like this and see the way such things work. At the same time, make sure that you give her the chance to talk about her fantasies and introduce you to some of them. If she is interested, progress to the next step. However, there is a hight chance at this point she will not be interested and/or even repulsed by the idea. You will have to live with that. This may mean she leaves you, this may mean you keep her but have to give up the dream, it may mean you leave her to find someone who is into it. Make sure you make that decision in a mature manner...

Step two, start small. You need to show her that it is fun and for this your best bet is to avoid jumping straight in at the deep end. Carry on your normal vanilla relationship but introduce some small kinky things into the bedroom. I have yet to meet a woman who is not turned on by light bondage and spanking (as I have said before, I don't know if this says something about women in general or just the women I meet...) so there is a high chance that she will appreciate the chance to experience both on a regular basis.

Step three. Most relationships remain at step 2 - a little kink in the bedroom. Even many vanillas reach this step. As time goes on you may find this expanding into more and more elaborate things but you are not 'a BDSM couple'. That is the step where you more formally accept each other as Master and sub. There are many different degrees of this and steps to get there and many fall between the extremes of 'kinky in the bedroom' and '24/7 Master/slave TPE'. Chances are you will find your own level based on your mutual fantasies and real life situations (for example, you may not be able to have her kneel to eat dinner if the in laws are visiting ). If she is interested and naturally submissive, then you will reach a point where this occurs.

But, as stated above, you do need to differentiate between a 'bottom' and a 'sub' and even a 'slave'. There are lots of discussions on this topic in the forums so I suggest you read through some of them. And submission and submissive as well... Maybe your first step should be to research what you think you want and see if you really do want it. it can be a lot of work and responsibility looking after a submissive.