How do i get to talk to the prostitues on assassins creed 2 for cover

First off you must reach a certain main mission in the game, which gives you a tutorial on how to use them. It is the mission where you meet Paola, the owner of La Rosa Colta.

If you are literally asking how and you have already passed this mission, go up to the courtesans and press triangle if you are on PS3, or Y if you are on Xbox.