Hi.
I have received at least 15 questions exactly like this one. So, I guess you are not alone. French kissing is just like anything that you have never tried; it can be scary until you do it enough to feel confident or to even appreciate it. But there is no one way to french kiss and everyone has their own very personal likes and dislikes.
I think it is very fun and there is no need to feel anxious or worried about someone dumping you.
I think knowing what to do comes pretty naturally or at least you have to believe that it does. It is an insanely awkward position to suddenly have this other tongue in your mouth for no good reason. So it is better not to think about it too much and just follow your instincts (even if you are just pretending that you have some).
I think the only important rule is to not shove your tongue in too much at first. Slow kisses are good for starters.
See www.teenadvice.org which has teenagers talking about kissing and also our kissing section in the gURL sexuality series.