Log in to your webmin, make sure to use the user with all permisions or the super user account.

Next is click on “system” and then choose “users and groups”.
Click create a new user, enter your username, leave homedir in automatic, let webmin pick the user id, select as shell /bin/sh, click on “normal password” and choose a password, leave all other as webmin is offering, and ckick create.

Finally use any of your favorite ftp and you can now access to your FTP.

enjoy!
-Jdam