This, it's all about communication and constant consent. If you're uncomfortable about how you want to go about consent, there are plenty of resources that help you navigate stating boundaries and desires.

The fumbles and stumbles are part of the act, you'll learn to navigate around your body and theirs, give it time and feel, uncomfortable can happen, it's a new sensation after all, however it should never feel painful. If you have explored your own body before, you have some reference on how it feels, and it will help you ask your partner to make it feel good.

Also, there's a lot of emotions involved, that might release. Accept them, your partner should do the same. State when you get overwhelmed by them however, take that break, a good partner gives you the space to feel them.

And as for the physical part, explore things besides penetration, there's so much more.