My friend and me are connected via LAN router, and we both have Ubuntu 12.04. There is a problem with network. My friend can see my computer on network, but I can't see his computer. I can ping him and connect to phpmyadmin (he has PHP server installed) but I can't access files on his computer? What seem to be a problem?
According to the comments above I would:
(where you substitute remote-user with the username on the other computer and the IP address)
If this works, it should ask you for a password and allow you to login.
After installing ssh, you can probably use SFTP to access files on the remote system. Open nautilus, press CTRL+L, it will show the "location bar", where you type:
It should ask you for a password.