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.