When you have registered a profile, you can not only browse and watch models but also join a group chat. If you want to whisper to a model, go to the Chat Settings option, it's a small button near the message bar. In the list of options, choose "Type in Whispers Only". Once selected, you can send whispers to a girl. If you want to whisper to other Flirt4Free models, you'll have to enable this very function every time you switch to another girl's profile.