First, tanstaafl, if you could, please move this to the help forum
Alfredo, people are working on editing the documentation on the website so hopefully things will be clearer eventually.
You don't have to create a new account; you can use the default settings.
As for the old passwords, well, I'm not sure why you would want to keep them. The general idea is that PasswordMaker creates new passwords for you while you just have to remember say, one Master Password.
So, you would want to replace your old passwords for your various accounts with new passwords.
If you wish to use an old password and want to use PasswordMaker as your "password manager" then there is a workaround for that... the following is what I think it was, but you can search the forums for this or perhaps someone else can correct my errors...
...you can create a new account, make the "generated password length" the exact length of your password, and enter the password you want to keep as the "password prefix" so then PasswordMaker will now just fill in the prefix/"password"
the "password length" and "prefix" are both on the new account window which you have to create after creating a group besides the "Defaults" group