trying to use the seahorse password manager
 

Using pop os and seahorse for opening websites I use every day. Can it be used to enter user names as well as their passwords? Or would a browser extension program work better for everything but login?

I haven't used seahorse in some years and thought it was for storing encryption keys. But, for password management I use Bitwarden as a Firefox extension. Look in the Add-ons for it and others.

For saving usernames and passwords I'd go with Keepass. It's good for storing credentials, opening the websites (no risk of entering the wrong details into the wrong site!) and generating passwords. Your save file can be encrypted and unlocked with a keyfile or Yubikey too. It works really well!

I have been using KeepassX for about five years and recommend it highly. Its databases are also compatible with Keepassdroid for Android phones.

I used KeepassX as well but stopped since its development doesn't appear to be very active (last version was on 10/2016)...
I recommend KeePassXC (https://keepassxc.org) instead.