The Item Collector sucks up any items which are dropped in an area between 1x1x1 and 11x11x11 depending on what radius it is set to. It sucks up the items from the side with the black hole and deposits any items in a Chest or another block with an inventory which is placed at the opposite side (Where the arrows point too). It will not suck up any items if it doesn't have an inventory to put them into. Right Click on the Item Collector to access its GUI where you can change its range.