If you need to login to the app please see the support article Logging Into the HikCentral Client for Windows.

Once you are in the app you will click on the menu icon in the top right hand corner and click on Monitoring. 

You will then be on this page. Notated on the screenshot is a legend for the icons you will use. 

First, select the number of cameras you want to see at the same time. 

Once you have that selected, then on the left hand side of the page click on the dropdown and drill down to the camera you want to view. 

It will look something like this.