Island is basically a big computer program that takes in buy and sell orders from lots of sources and matches them up when ever possible. It also ha a number of ways that is displays the open orders to the out side world with the intent of soliciting someone else to enter a matching order.

For a number of regulatory reasons, retail investors can not enter orders directly into the Island system. Instead, a retail investor would typicaly give the order to thier broker who would in turn enter it into Island.