Each time you login to TFS using Teamprise Explorer you will need the following information. (Check with your TFS administrator for the exact URL and portal.)
Name for your TFS workspace (Teamprise automatically assigns the last workspace you used; to change TFS workspaces see, Changing workspaces in the Manage Workspace section.)
You do not have to exit Teamprise Explorer to login to the TFS. In fact, you may want to login as a different user or you may want to log in to another TFS. In such cases you can use the Teamprise menu to invoke the login dialog box.
From the main Teamprise Explorer menu, click File > Connect to Server...

In the Connect dialog box, enter the values for your server. If you check the Store Password checkbox, the values you enter will be the default, so that the next time you chose Connect to Server from the File menu (or when logging in again from a launch) the last values you used will be included. Click OK.

If you wish, you may create profiles if you frequently connect with different settings. To create a profile:
See Related
Before you begin
Creating and removing a TFS workspace