Using source control
Microsoft Team Foundation source control provides source-code version control functionality, which can scale to handle thousands of developers.
Source files are stored in a source control system repository (a Team Foundation server). Team members check files out to working folders on their computer, make changes to the files, and check them back in. When a file is checked back in to the repository, the source control system makes a record of the change between the new version and the previous version. When checking in a file, the team member adds a notation to the file's record in the repository so that others can see what changes were made to the file. That way, if someone makes an unwanted change to a file, you can revert the file to an earlier state.
For more information, see Checking files in and out.
A file can be checked out by more than one person at a time. After the first person checks the file back in, subsequent check-ins will go through a merging process to resolve any conflicts. For more information, see Using Team Explorer and Working with Team Foundation Version Control on MSDN.