How do you finger a girl while making out?

If you are sitting down, start kissing her a little harder. Then, if she gives back, slowly slide your hand up her leg. If she says stop, STOP. It may be going to fast for her. Once you reach her upper upper thigh, touch the top of her pants with one finger. Slowly increase the number of finger. If she is still okay with it, slide one finger inside her pants. At this point, she will be trying to make things easier for you. She will probably spread her legs out and lean her crotch up. Add more fingers, then stick your whole hand down there and pull down her pants a bit. Move your fingers down and touch her in a way she is confortable with.