Before you can check out an item, you must add it to the Team Foundation source control server. For more information about how to set up a local workspace and adding items to source control, see Walkthrough: Working with Team Foundation Source Control from Command Line.
Unlike some source control systems, Team Foundation does not get the latest Team Foundation source control server version during a check-out operation. Instead, it makes the current workspace version writable. For more information, see How to: Get the Source for your Team Project.
You can use tf edit as an alias for checkout.
By default, multiple users can check out the same source-controlled item at the same time. When you use tf to check out an item which has pending changes in another workspace, information about the nature of their change is printed on the command line. In most collaborative development environments, the probability that you will make a change in your workspace that represents a potential merge conflict with a pending change in another workspace or vice versa, is unlikely. Most conflicts that do occur can be resolved automatically by Team Foundation. For those that cannot be resolved automatically, you can use the Resolve Command to safely decide which change, yours or theirs, you want to keep. If you are concerned that another user might make changes in their workspace that conflict with your pending changes, you can use the Status Command to monitor other workspaces for newly applied changes. Alternatively, you can use the Lock Command to prevent other users from checking out or checking in until you have checked in and unlocked your own changes. As a best practice, use the lock command with discretion and notify your teammates why you are doing this, and when you plan to remove the lock.