in console:
adduser username
(choose a password)
--------------------
open /etc/passwd in geany
change the last line to
username:x:1000:1000:Linux User,,,:/path_to_ftp-folder/:bin/bash
--------------------
make username the owner of the folder by typing:
chown username foldername
Start PcurlFTP file sharing and choose to share a folder
choose username/password but NOT to allow root connections (bottom option)

portforward port 21 to internal IP in router
--------done----------

To change password for ftp user type
passwd username
(choose password)