Beginner confused about networks

Hi all,

I’m fairly new to crypto and find the networks quite overwhelming.

I can choose from Ethereum (ERC20), Optimism, Arbitrum One, or Base network.

Unfortunately I do not know the difference between these - all I know, is I don’t want to pay the exorbitant fees from the ERC20 network.

Can I just randomly choose the same low fee network on my sending and receiving end, or is there a process to using other networks, e.g., buying supporting coins for a transaction?

I also noticed the differing networks have their own amount of eth storage. If you send eth using a specific network, it’ll stay on that network forever? You can never combine all your eth?

Are there any negatives of using different networks to avoid exorbitant fees?

As you can see, I’m quite confused, any help would be much appreciated!!

Thanks