I'm probably overthinking this (I'm good at that), but I got dragged into a campaign that I was reluctant to play in because I haven't played in years. The people I used to play with were great, but they were pretty bad at explaining rules and parts of the game I didn't understand, which was quite a hefty amount. I caught onto a little bit as we went on, but that was years ago. In this new campaign, I'm playing with a DM who's already talking about kicking characters out if they're not good enough, even though we haven't even made them yet; we're doing that this weekend. I'm worried that because it's been so long and I don't remember much, I'll be on that list. I've done some research already, but I'm honestly so lost and confused on what I'm reading. I'm not even sure what the campaign is-- something about vampires and an island.
Most of my confusion is about fights/battles/whatever they're called. Encounters? Anyways, spell slots have me in a chokehold, and I cannot comprehend most of what I'm reading about them. This was my major weak spot the last time I played, too. I would appreciate it if someone could break them down in a simple way, or recommend a source that could explain them. I want to do good in this, but I don't want to have to look up how to play in the middle of a session. Any help is seriously appreciated.