You dont "get them" you either manually change them or you gain "points" to level them up
Preferences determine how much lust you gain or lose when someone is doing something to you
Example
Lets say you like to get pegged, the preference should be Anal(bottom) (and the level, lets say you have it on "Loves") when you do/someone does that action to you resist less and gain more lust
If you hate, lets say, lactation and the npc puts pumps on u, the lust metter should start to go down and the resistance % will start to go up
This also changes the satisfaction % at the end btw, so keep that in mind