Cover 2 Defense in football gets its name from the two safeties playing deep zones on the field. The two deep zones in this formation refer to either half of the field. The Free Safety (FS) is responsible for the routes on the left side of the field and the Strong Safety (SS) is responsible for the routes on the right side.
As stated above, there are 2 safeties in Cover 2. Each safety plays about 15 yards above the line of scrimmage and always need to be deeper on the field than the deepest receiver. FS is responsible for the routes on the left side of the field and the SS is responsible for the routes on the right side.
The Middle Linebacker (MLB) has a very important role in Cover 2. With both safeties split out wide and covering the outside, the middle of the field is completely open. The MLB has a "Mid Read", meaning they start but covering the short middle of the field. This includes covering closer to the line of scrimmage and seeing if it is a run play or play-action pass. MLB is responsible for keeping their eye on the QB. Watching the QB will tell them where they should be on the field. For example, if the MLB sees that the QB is throwing over the middle of the field, the MLB must make a cut off the route they are covering, and try to either tackle the receiver right away or get there in time to make a play on the ball. Compared to the MLB, The Outside Linebackers (OLB) drop back into coverage right away, each one headed to the opposite outside hash marks. They are there to cover a deep flat or curl zones. One of the OLBs or MLB will sometimes line up across from the slot receiver.
Cornerbacks, or Defensive backs (DB), typically cover the flat zones and start on the field facing the outside wide receivers across the line of scrimmage. Before the DB begins to cover the flat they usually play press coverage and check the Wide Receivers (WR) at the line of scrimmage. This contact at the line gives the safeties a head start on backpedaling down the field to position themselves that no receiver will be behind them.
In Cover 2 Man, the FS and SS maintain the same two-deep zone coverage. The Defensive Backs, however, now play strictly man to man coverage on the wide receivers. The MLB in this Cover 2 concept, also switches to man coverage normally covering either the tight end or running back and the OLB taking the other.