Grand Theft Auto 4 Hos?

I paused my game and went into the stats section and into the money area and it says money spent on everything it also says money spent on prostitutes $0 and Given to tramps $0 i didnt know i could go and get a ho does anyone know how i can do that. I see hos in the street but when i walk up to them no option comes up for me to do anything. Also in the MISC area of the stats it says prostitute visits 0. Where do i go and what do i do to see these hos and do whatever with them. I want to suck every bit out of this game and this is the only thing i havent done.