Here's a great rundown of sexual anatomy that might give you a better sense of your body: With Pleasure: A View of Whole Sexual Anatomy for Every Body
. If you haven't done this before, you may find it additionally helpful to use a compact or small hand mirror to give yourself a look at your genitals; it can be easier to find everything mysterious and scary when you don't have a visual idea of what your body actually looks like.
Here's an article about handling pain with intercourse: From OW! to WOW! Demystifying Painful Intercourse
. The information here can also be useful for experimenting with a toy or your own fingers in your vagina, also, in terms of thinking about how to make pain less likely and how to deal with it if it occurs.
I think these two are a good place to start; give yourself as much time to read through them as you need and if you have questions afterwards, we'd be happy to answer them!