To add files to the source-control system:
  1. In the Project Explorer, select the file to add. If you select a folder, project, or solution, any eligible child items will also be added to source control.
  2. choose Source Control > Add or press Ctrl+R, A.
  3. The dialog will list the files that can be added.
  4. In that dialog, you can deselect any files you don't want to add to source control.
  5. Click Add.

Files are scheduled to be added to source control and will only be committed to source control (and seen by others) when you commit the file.

Enabling the VCS > Options > Add Immediately option will bypass the dialog and immediately add (but not commit) the files.