What is checkout and checkin in document systems?
“Check out” and “Check in” functionality is something like elements of SVN system. Imagine that you have a document. And two users, which has access for editing this document. And they want to be sure they are working with up-to-date document, and don't prevent each other from editing this document. So, “Check out” and “Check in” functionality is the thing, which helps them with it. When user1 starts editing the document, he\she checks out it. So, for the system it is some kind of mark that this document is "busy" right now. And after editing, user1 checkins document, and after that all the changes he\she has done are now available for user2. Since this functionality is very complex, there are o lot of scenarios this functionality can be used. For example, if two users start editing a document at the same time, and then user1 checkins document one minute before user2, then user2, when trying to checkin document, will the message that his copy is not up-to-date, so he\she has to take new copy, before committing changes of a document. And, yeap, as WJCarpenter mentioned, you have to work with infocenter to get the full understanding of what checkin\checkout is.