Just add a user with the useradd command to your system, e.g. like this:
useradd -d /home/exampleuser -m -g users -s /bin/bash exampleuser
This creates a user exampleuser
with the homedir /home/exampleuser and the shell /bin/bash (you can also use another shell like /bin/false (which means the user has no shell access which is good security-wise), but then you might have to add the shell to /etc/shells). Then run
to give that user a password. Next make sure you have
in /etc/proftpd.conf. If you have to modify /etc/proftpd.conf, restart Proftpd. Afterwards, you can use an FTP client and login with the username exampleuser
and his password. That user will be chrooted to his homedir /home/exampleuser.
If you don't want to use system users, have a look at this tutorial: http://www.howtoforge.com/proftpd_mysql_virtual_hosting
It uses virtual users which means all you have to do to create a new user is to add it to the MySQL database.