No matter what you want to do with your linux server, you will always have to open a port. Just about every service uses a port, whether it is web or game server software. This guide will help you edit the IPTable file on CentOS and Ubuntu.
Optional: SFTP/FTP client
First off, connect to your linux server.
Open the terminal and type the following:
You will need a program since the command prompt, or CMD, lacks the „ssh“ feature. I recommend using putty.
Under „Host Name“ enter either the IP Address of your server or the (sub)domain. Port should be 22. A nice feature with Putty is that you can save your settings, so you can quickly connect to a server without having to retype everything. Hit „Open“ and enter the username when prompted.