Ftp servers are used to transfer files.
Once logged in with a login/password, it is possible to move through the directory tree to upload/download files.
By default, the protocol is optimised for text files. Do not forget to activate the binary mode if necessary.
A guest or anonymous account allows on certain servers to freely download public documents.
The login is 'anonymous', the password is conventionally the guest's email.

$ ftp 10.0.0.11
Name (10.0.0.11:yolo): anonymous
Password: yolo@yolospacehacker.com
ftp> pwd 
ftp> cd docs
ftp> ls 
ftp> bin
ftp> get flag.txt
ftp> put backdoor.php
ftp> bye