The item net catches and stores ocean debris that floats into it. There is no limit to how much ocean debris it can hold. Once there is some ocean debris trapped in it, one can press their use key on the net to collect the items. Sharks can destroy item nets if they bite them enough, and there is no way to repair the nets without replacing them when they are destroyed.
The item net can be placed adjacent to any foundation or other item net.
The item net appears to be four sticks tied together in a square shape with rope, with two planks on one side for easy access. There is a net attached to one of the planks which catches the ocean debris that drifts into it.