When working in a collaborative environment, you can check out and check in files when transferring them between a remote server and your local computer. See Checking in and checking out files on a remote server.
Checking out a file is the equivalent of declaring "I'm working on this file now—don't touch it!" When a file is checked out, Dreamweaver displays a check mark next to the file's icon in the Site window. A green check mark indicates that the file was checked out by you, and a red check mark indicates that the file was checked out by another team member. The name of the person who checked out the file is also displayed in the Site window.
Checking in a file makes the file available to other team members to check out and edit. The local version becomes read-only to prevent you from making changes to the file while someone else has it checked out.
Note: Although you don't need to know this to use the check in/check out system, in case you're curious, Dreamweaver keeps track of checked out files by placing a text file with the extension .lck on both the remote server and the local site. The .lck files are not visible in the Site window. Each .lck file contains the name of the user who currently has the file checked out.
Dreamweaver does not make checked-out files read-only on the remote server. If you transfer files with an application other than Dreamweaver, you can overwrite checked-out files. However, in applications other than Dreamweaver, the .lck file is visible next to the checked-out file in the file hierarchy to help prevent such accidents.
You can enable check in/check out for some sites and disable it for others. See Setting up the check in/check out system. For information about transferring files between local and remote sites without checking them in or out, see Getting files from a remote server and Putting files on a remote server.