As a goalie, I want all my player to play well defensively and be responsible in our own zone. To win a hockey game, you need to play a good defensive game to limit the scoring chance against you.
The wingers needs to look at the defenders so when they have the puck, they have a constant pression against them. Not that complicated, but it's important too because defenseman have a great impact on the offensive side too and you need to limit their support.
The center have to help his defenseman so it's a 3vs3 in the zone so everyone have a player to look at. After his team get the puck, he needs to help getting on the offensive side so he get no rest. Always moving his skate to be ready when it's time to be on the offensive.
So that's mainly their job, that and hitting the guy who have the puck haha!