Your content reports are statistics about your videos.
By using the date interval on your top left you can specify between which dates your statistics will show. By default it is the last 30 days.
Plays means how many that have clicked play on your videos.
Player Impressions means how many have seen the player of your video regardless if they clicked play or not.
Play to impression ratio is how many who click play on your video by how many who saw the video player.
Drop-off is how many people who have seen up to a certain point in your video.
If you click on a video in the list you get statistics on a particular video.