A unique feature included with WHMCS, is WHMCS Connect. With WHMCS Connect, you can easily manage your servers by accessing their control panel with the click of a button (rather than having to enter in credentials each time).
How To Access WHMCS Connect
Step One: Log into your WHMCS Dashboard
Step Two: From the WHMCS Dashboard, in the top menu navigate to Utilities -> WHMCS Connect
Step Three: From this next page, you will be able to see a list of all your added servers on the left side of the screen by default. You can also filter through the Servers based on Name or group as well.
Step Four: Find the server you are wanting to connect to and simply click on it from the list on the left side of the page. If setup correctly, the Larger Window on the right will display the Control Panel or in most cases, the WHM of the server.