I can't understand L2 networks no matter what

So my current understanding about roll-ups is that since eth gas fees are like really high per transaction, so it would be much better if the transactions are bundled and submitted as a single transaction , but like how does this work? say if we take optimism for example , like a lot of nodes are running for that particular L2 right and if I make a transaction to that network , it will be bundled with other transactions and submitted as a single transaction to the main network? is it like that?

If say bob sends 1 eth to Alice , like how does this work on roll-ups , first the optimism nodes do the work on verifying stuffs like the balance and other and what do they do ? submit it to the main network?

And how do they submit, like via rpc to a contract or smtn?

please help, I can't find a source that goes into technical details of this other than than blog posts saying what are L2s and how they fix the eth scaling issues.

Edit: It finally clicked for me , huge thanks to u/DepartedQuantity for helping me out.

So here's my understanding:

Till so far in my mind was that the rolling up is for the L1 transactions, since transaction fees are higher so send the transaction to a separate network and let them batch up multiple users transaction together with mine and submit it to the L1 as a single transaction with some proofs. And some smart contract does some magic and everything is good but it doesn't make any sense because someone either way has to pay to change the state on the main chain which is going to be really expensive.

But the thing is that the L2 is a network own it's own with an evm and state changes and etc etc. Connected to the main chain with bridges so an equivalent on chain can be given in the other. And all the transactions happening out there is independent own its own and what it submits to the main network are transactions details(or whatever) in L2 so if something ever happens to it , it can be recovered.

And not L1 transactions that are verified off-chain and submitted as a batch to the main chain.