How do the current usernames and passwords get transferred to 1password?

Hi there @peggy555777 :)
Welcome to 1Password! Things can be a little daunting at first so let me see if I can break it down for you.

First off, your Secret Key. Your Secret Key works in tandem with your Master Password in order to protect your information. Think of them as two pieces of a key needed to open a lock. Realistically, though, you don't need to worry about memorizing your Secret Key. It is only needed when signing in to your 1Password account on a new device for the first time. Let's say you try to sign in to 1Password on your phone for the first time, or you get a new computer and want to log in there. You will need your Secret Key in order to do that. After the first time, only your Master Password is needed. So don't worry too much about it. Just keep your Emergency Kit safe and refer to it when you need to.

Second, entering your passwords and such into 1Password. That's where the browser extensions come in. Any time you sign in to a website, 1Password will ask if you want to add the log in to your vault if you haven't already. You could add them manually, but doing it through the browser is far easier. Keep doing this with your various websites and eventually they will all be transferred to 1Password. More information on how to use the browser extension can be found here

I hope that helps. If you need anything else clarified, I'm always here to help. :)