Media usually show ingress story and events. Some people like to collect them. Currently there is a series of lore games, and some medias are clues and pieces. There's aren't actually anything useful for gameplay, you can recicle them all.
To get on scoreboards you need to make large amount of Mind Units, the points you get by making control fields.
Agreed. There is no “Leaderboard” for The Investigation related things like the Tessera. There are “First Discoverers” for each Tessera but there really is no awesome individual benefit.
The Leaderboards are for Ingress itself as a game, creating fields and capturing MU.