By default, Help+Manual will automatically check your topics out of the Visual SourceSafe (VSS) repository when you edit them and check them back in when you save and move on to another project.
If you wish, however, you can also configure your project for manual check-out and check-in. Then your project will be displayed in read-only mode when you open it and you will have to check out your topics manually in order to edit them. You must also remember to check your topics back in again when you finish your work, otherwise other users will not be able to check them out for editing.
When you are working in a team all the team members should use the same check-out mode. Manual mode provides maximum security because then the TOC is also protected against editing conflicts.