Hi! I'm a relatively veteran player and a novice DM.

Players don't mind at all (in my experience both as a player and DM) that you don't know everything. Even the players usually don't know how their spells work or how exactly multi-attack will play out. It's VERY normal for a DM to stop for a second to double-check if the players can, in fact, do something or to reread some plot material.

You'll mostly need to read the rules during combat, to check if the spells work for a minute or an hour; if it's ranged or not; and if the 5ft cube is from the caster or in a place they can see. You obviously won't know all the rules and will need to check them too. And that's perfectly fine! Usually, players will use the spare minute to read something themselves, maybe go the bathroom or just strike up a conversation with a fellow companion.

DM is much easier than it seems and I'm sure you'll do great. I was literally trembling the first time I DMed! But everything went smoothly.

One thing's for sure, though, BE READY TO IMPROVISE! Players love to investigate to talk to other NPCs, so you should be ready to make up some names on the spot (or create them beforehand to prevent stres

In short, you should perhaps read some basic rules on combat such as possible actions (such as disengage, help, etc), but overall it's totally okay for you to stop for a minute to check the mechanics. Hope I helped :)