Hi John,
generally, it’s highly recommended to use different passwords for everything (i.e. not just for WordPress, but also for user accounts on different websites). The reason is that if an intruder gains access to one of your accounts by cracking the password, they can do much more damage by trying the same password with your other accounts — whereas if every account has a different password, the damage is at least somewhat contained.
Most of us struggle to remember passwords — especially when they’re also supposed to be “strong” (i.e. fulfill certain criteria that makes them harder to guess). That’s why a lot of us use password managers. Your browser probably has one — it should normally appear in the top right corner whenever you enter new credentials for a given account for the first time (i.e. when signing up), asking you if you want to save them, and later offering you to fill them back into the account’s log-in form.
Alternatively, there are dedicated apps that also work across desktop and mobile devices.
There are a lot of good online resources on the Why’s and How’s of password managers — see e.g. this New York Times article.
Hope that helps!
