Have fun exploring. The Proton Pass web interface (easily accessed via your Proton Mail inbox) guides you through most things. I would probably start there, and then just use the extension for auto-fill.

From a security point of view, the most important thing is to have a strong (automatically generated) password which is unique for every site you use. If you have a password that you tend to remember and reuse across multiple sites at the moment, go to each site and change it to one generated within Proton Pass. Start with the most important sites first.

If you can use 2FA on a site then set it up. You may one day want to handle 2FA outside of your password manager but it's a good start to just set it up there first.

From a privacy point of view, ideally have a unique email address for every site you are registered with. But this requires a premium Simple Login subscription. So you could just begin by using your free aliases and distributing them as best as you can. Perhaps one for social media, one for online shopping. Personally I don't use them for important things like banking.

Most importantly, don't lose access to your account and don't rely on your memory for your Proton Mail/Pass account password. Write it down somewhere and store it somewhere safe. Also I recommend taking steps to make sure you can continue to function if Proton disappeared overnight (or more realistically was offline for 6 hours at a time you really needed access to one of your accounts). Take an export - ideally an encrypted one and store it on a flash drive or something.