[otrs] newbie question about link

Can anyone explain me what "link" means? I tried creating parent, child and normal links and nothing happens... Is there any way to "include tasks" into a ticket? I mean, I move a ticket to software qeue, for example, but in order to close the ticket, support department must "do" several things and if all of the "things" are not "close", we cannot close the ticket.... By the way, sorry for my english...