Comment 1 for bug 1531495

This sounds as if you have a couple of issues here.
To get started with a fresh installation of the application, please note that the application preferences are stored in ~/.local/share/geary/ There should be folder(s) for the account(s) you created previously. If you want to configure the same account a second time, please delete the corresponding folder first.
The passwords are stored in the keyring application. You could check if something is stored there.

When there is only one account configured, the "-" button is grayed out. This works as designed.