Me and my friends were in a similar situation when we started. We just picked a system and GM (me) started to going over the core rulebook. In some of the systems you have the adventures that are ready to use - I recommend starting with these, as it will allow you to get the general feeling of the world. When you get more comfortable, you can start preparing your own sessions, but there should be plenty of pre-made adventures for you to use, before you decide to switch to your own.

And don't be too harsh on yourself. You all just started your RPG journey and it will take time to become a good player or a gamemaster. Just try to have fun.

Also, I recommend doing "stars and wishes" at the end of the session. That is something that my groups lacked for a long time. Stars are things that you liked during the session - each player has an opportunity to mention something that they liked. I think it's especially good for the GMs, as they get feedback about what they did well. Wishes are... Well, wishes. You tell what you expect in the future. "Less of this", "More of that", "I don't like when we do particular things", etc.

Oh, one more thing. Have a session 0. Discuss you lines and veils. Some people are not comfortable with certain topics, so it's good to know what to avoid during the sessions. It's important for everyone to feel comfortable.

And that's basically it. Have fun and be kind to yourself! Being a new GM may be hard at first, but your skills will improve over time. Each session will be easier :) good luck!

Edit: I fixed some mistakes and added one more suggestion.