If you are behind a firewall you will need to open port 8080 to connect to the TFS Web Services. 

You might also need to add a host entry of your team foundation server in C:\Windows\System32\drivers\etc\hosts  IP   Hostname.

After you have done all of this, go into the team explorer tab and click add and you will be able to add the server in the dialog that comes up.
To add files you need to add a workspace and set the working folders.  A workspace represents the client computer you are currently working from.  If you are a perforce monkey then you should know that term:
-Go to File>Source Control>Workspaces
-In working folders click where it says "Click here to start a new working folder ..." you must be connected to the VPN.
- Click ...
-Choose the repository > Click OK
-Specify the local folder by clicking the '...' under the local folder section.
-Click OK and then close.

Now when you go to View>Other Windows>Source Control Explorer, Browse to the folder.  You will now have the option to add files indicated by the file with the plus sign, in the buttons at the top of the source control explorer.

Let me know if you have any questions.

Thanks,
Tommy