Someone ELI5 layer 2s

I bet this had been said before but I want it explained again.

I understand how eth works and is secure and keeps track of things. The thing I don’t get is how a layer 2 is secure. I understand it basically does an entire group of transactions at once to reduce gas fees but I don’t understand how it maintains Ethereums security.

I have my wallet and my keys right? Do I give them those? Are some type of zero knowledge proofs used so they can use my address and make transactions as me but without knowing exactly what my keys are?

Do I make a new wallet in their network and somehow that wallet is safe, but how is that different than a CEX?

Unless I’m misunderstanding layers 2s are centralized right? They are a single group processing transactions before it gets to Ethereum and then tells eth what to do at once. Why can we trust this group and who is keeping them honest and secure if it’s not decentralized.

I feel dumb because I’ve been following ethereum for some time now and still don’t get this. Why are layer 2s safe. If the answer is zero knowledge proofs (i assume it is) can someone give specific examples for me to see how it actually works with eth?