By default, ProFTPd will accept logins from the system users (except root). You will need to create additional users on the system to gain FTP access and/or set up non-system users.
It is beyond the scope of this document to cover both, however useful links can be found at the following URLs:
To see how to chroot a user, see the below:
To create virtual (non-system) users for ProFTPd, see here: