ok half the people in here don't know shit lol but the first time is somewhat hard for a guy.
First of all make sure you protect yourself.
Second make sure you get her a little wet before trying to ram her or else it'll hurt her.
And most importantly, it is not just gonna slide in, you have to first find the hole with your fingers, then guide your penis with your hand and use a little bit of force to get it in. Once it's in, you should know what to do
* I forgot to mention, some guys, like me for example, tell the girl to put it in for them the first couple of times. Don't be embarrassed it makes them happy that they're taking charge and relieves the stress of you not finding it.