>>81704701
You don't need to understand it all at once. Break it down into smaller steps and practice one at a time. Start with eyes, then mouth, then body, etc. Don't worry about what you are going to say, just listen to them and then you can respond when they are done speaking.
If your only problem is dealing with girls then you are probably nervous and inexperienced. Unfortunately all you can do here is practice. Just talk to a lot of people, men and women, and you will start to improve. Worst case scenario just tell them you are an autist and are practicing your social skills; most people will be fine with that.