Each line will contain the following (from left to right):
Preview picture of content: This is a preview created from the currently assigned content to be played on the device.
Check each box to multi select: Use these to select the multiple devices that you want to send the next iteration of commands to.
Device Name: This is the current hostname for each device
Device IP: This is the current assigned IP for each device
Individual select button: Use this to select only the device in this line, you well then be taken to the Main Panel for JUST that device.
Select 1 as normal: This will not show a number, only the information of the selected device in the preview panel.
Select 2 or more but less than All: This will show just a blue number for the amount of devices selected.
Select All: This will show the number of devices and a star to indicate ALL devices.