People who take the active role in a BDSM "scene" or session are referred to as "tops", and the person they do BDSM to, as "bottoms". So we talk about tops that are good at
putting people in bondage or using a flogger, and bottoms that can take a severe caning or who like to be fisted. (Some gay men also use "top" and "bottom" to refer to who
penetrates who, but in BDSM the terms are completely general and not limited to sex.) Many people enjoy being both and are said to be "switches".
The other dimension is dominance and submission (D/s). The person who is in charge is the "dominant" or "dom", and the person who submits to them is the "submissive" or "sub".
Most of the time, dominants are also tops, but this isn't always the case: some dominants have no interest in doing physical BDSM like bondage or flogging to submissives; and many
tops don't want to be in charge. A useful rule of thumb is to see who it's being done for and who is making the decisions: if that's one person, they're the dominant. A good example
of this are "service tops" who inflict bondage or SM for the benefit of bottom and pretty much to order. Many service tops are submissives when they form D/s relationships.
What is "Informed Consent?"
Informed consent is the condition under which the people involved in any BDSM activities are aware beforehand of the meaning of each term,
the prior agreement of all participants of the limits to which each activity will go and the agreement of safe words which will bring the activities to an immediate halt.
No-one can give "Informed consent" if they are under the legal age of consent in the place where the activities are carried out.
No-one who is classified as a vulnerable or at risk adult can give informed consent.
Many people fantasize about some elements of the BDSM scene but very few like or want to be involved in all of them. Like everything in life choose what you want to do and leave the rest,
Never get involved in any activity that you find unpleasant or which you do not want to do.