When you have edited and saved a document and are no longer using it, you should save the changes on the server with the Check In function. After this, other users will be available to check the document out and edit it. The easiest way to see all documents checked out to you is to open the Checked Out to Me view, which can be found in every document vault.
You can easily comment on changes you made when checking in an object. The Check In with Comments option opens a text box for entering a free-form description of the changes you made. The comments are displayed in the Comments view of the object's metadata card.