Sometimes you only have one, you have to run your channel programing to see IF you can get more, though nowadays you are required to have a cable box or a DVR to be able to receive signal to watching anything more than your local few channels.
Take it you read the manual that came with it.
It will tel you how to use the menu and setup of the tv.
If you are talking about free view and why you only get three channels detected.
It will be because the aerial on roof is old and poor, or out of alignment.
To receive a good strong enough digital signal.