How do I add a user to FTP which relates to the Linux Username and PW?

Hi I have enstablished a ftp localhost connection and it's asking for a username and password, I haven't created one.. I just put the Linux username and password (the one when I access to linux) but returns the following.
I would just like to use my linux account username and pw to access the ftp, how can I do this?

itad@itad-virtual-machine:~$ ftp localhost
Connected to localhost.
220 (vsFTPd 3.0.3)
Name (localhost:itad): ITAD
530 Please login with USER and PASS.
530 Please login with USER and PASS.
SSL not available
331 Please specify the password.
Password:
530 Login incorrect.
Login failed.