Requiring check-out prevents multiple people from making changes at the same time, which can create conflicts over changes and lead to confusion.
When someone creates
a new file or adds a new file to a library that requires check-out, the file is initially checked out. The person who creates or adds
the file must check it in before other people can see it. Check-out is also required to update information about the file, such as the title or when the file is due.
When check-out is required, a file
is checked out automatically when someone opens it for editing, unless it is already checked out. The editing commands notify the user that the file
is being checked out. For example, if you click the Edit in Application command on the shortcut menu for a file, you see a message that the file is being checked out.
When you check out a file from some programs that are compatible with Windows SharePoint Services 3.0, you can work with the file on your hard disk, even when you are disconnected. The copy is stored in your server drafts folder, which is, by default, the SharePoint Drafts folder in your My Documents folder. However, you can change the location in some client programs. Working on files on the hard disk is frequently faster than working with files on the server and enables you to easily continue working while you are away from the office.
When a file is checked out, no one can edit it except the person who checked it out. Its icon in the library changes to indicate that the file is checked out 
. When you rest the mouse pointer on the checked-out icon, the name of the person whom the file is checked out to appears in a ScreenTip. Changes that someone makes to a file while it is checked out are not visible to others until the file is checked back in. This is true regardless of whether the person is working on the file on their hard disk or on the server.
When you check in a file, you are prompted to enter comments about the changes that you made. If a library tracks versions, the comments become part of the version history. If both major versions (major version: A numbered copy of a file that has changed significantly since the previous major version. Each major version is identified by a whole number (1, 2, 3, ...) to indicate that it is published for a wider group in your organization to view.) and minor versions (minor version: A decimal-numbered copy (0.1, 0.2, 1.1, ...) of a file that is in a stage of revision or that has changed only slightly since the previous version. Typically, a minor version is not published for a wider group in your organization to view.) are tracked, you are prompted to choose which type of version you are checking in. Find links to more information about versioning in the See Also section.
To require check-out for files, you must have permission to design a list or library.
- If the library is not already open, click its name on the Quick Launch.
If the name of your library does not appear, click View All Site Content, and then click the name of your library.
- On the Settings menu
, click the settings for the type of library that you are opening.For example, in a document library, click Document Library Settings.
- Under General Settings, click Versioning settings.
- In the Require Check Out section, under Require documents to be checked out before they can be edited, click Yes.
- Click OK.