This defence works off two principles:
Never give the outside
Force the long ball option
The Mid who is defending the player with the ball in this diagram will track back diagonally and 'pull his corner'. The other two defenders (Link and Wing) will hold a bit more on their players but will also track back diagonally. The other 3 defending players who are 'shutting' will move across and defend their team mates inside. When the ball is with the other three players, the direction of player movement is reversed as is shown below:
Communication from the winger/link players is key because it's not always immediately obvious to a mid player who they should be covering. In the heat of the moment, players can forget who they should be defending.
When mistakes happen (and they will), always remember that the most important person to defend is the ball carrier. In these situations it's better to force the attacker to pass under pressure which could lead to a mistake.