To view all screens: In the main view (Where you see all computers listed) you can click "thumbnails" in the top right to see all screens

To view specific screens: Select the computer you would like to see (Hold shift and click to select multiple computers) so that they are all highlighted like the below

Then click "watch" on the right menu (Under the devices sub heading)

You can also click the preview window to open them

To view one in more detail left click it. To return to the overview click "Grid" at the top