What is RCON?
Rcon is a protocol for executing commands on the server without having direct access to the console.
Firstly before you can connect, you must make sure Web RCON is enabled. To enable it, visit the Settings tab.
And then enable it directly on this page.
A server restart would be required for it to take affect.
Install RCON Program
You will be required to connect to it from an RCON Program. There are several different ones available you could use. For this example, and as a reccomendation, you can download RustAdmin.
You can install it with the button directly on their website.
Connect via RCON
Once you have opened WebAdmin, press the Server at the top. And then press Connect.
Your server must be fully ONLINE to be reachable from RCON.
Then you are redirected to a Configuration page. Here you would enter your respective server information.
TIP: Your RCON Port && RCON Password can be found in the Settings tab where you enabled the WebRCON.
Once you have entered your data, you can save the configuration.
And then press Server -> Connect.
Then if connected sucessfully, you will be the Connected in green letters at the bottom.
You can now use RCON to manage your server! :)