Basically you need to have an informed consent conversation.
And when it comes to any kind of kink, that informed part is as important as the consent part. You both need to really understand what you're consenting to, before consent is given. This goes for the both of you.
This means talking about it. Be specific. BDSM is an incredibly broad topic encompassing an awful lot of fun and horrifying things, so consenting to a BDSM experience is effectively meaningless. If you two want to have a fun experience with this stuff, you'll need to have some honest conversations about what you each would like to do, what you wouldn't like to do, and what you expect to get out of the experience.
A lot of folks find that it's helpful to learn about different BDSM related kinks first. Read about it together, watch videos about it together. Not just pornography. Believe it or not, there are instructional materials available, and porn can be... misleading... to put it gently. This will give you two a place to start with conversations about specifically what you all would like to experiment with.
Some folks also find clubs and munches to be helpful educational resources. Check around online, it wouldn't be suprising if there's a local kink group that organizes social get togethers or classes for the particular flavor of kink that you two find an interest in.
Like most areas in any relationship, communication is key. It may take some practice to get comfortable talking about the kinky stuff, but it's necessary. And I do mean necessary. If it helps, start communication with the easier stuff and work your way up to the more advanced topics. What may start off as a series of somewhat awkward conversations may turn into a form of forplay with enough time, practice, and confidence.
Keep in mind that this will be an ongoing conversation. Consent can be withdrawn at any time, even in the middle of an activity. Always make room for that. Check in with your partner regularly during play. This is where most folks employ "safewords". The best safewords are simple, and easy to remember. I strongly recommend the red, yellow, green system.
- Red = Stop!
- Yellow = Slow down, use caution, ease off.
- Green = Go!
Another option is the use of simple hand signals. Thumbs up, thumbs down. (For cases where verbal communication is more difficult)
I'm tempted to plead the fifth when it comes to backing this one up... Let's just say that, yes I have had these conversations in a number of different situations, and this answer is based upon some very personal experience.