On the main FAQ page for SO it gives a brief overview of what abilities you gain at different Rep levels (with more detail given on the official Meta-based FAQ for SO). One detail that should probably be added to both of these is a clear description of what you can do regarding commenting at the starting level of 1 Rep.
I've often seen situations where new users don't realize they can post comments on their own questions as well as any answers they receive, probably because the FAQs say you need 50 Rep to comment (so they don't even bother to try). This usually leads them to add their comments as answers, making a mess of things.
Perhaps the main FAQ page and official Meta-based FAQ for SO could have the following modifications made to their lists of Rep-thresholds for abilities:
- +1 (default) Ask or answer questions, comment on your own questions (and their answers)
- +50 Add comments to any post
UPDATE: It looks like some helpful modifications were made to the list of Rep-thresholds on the FAQ page, so I guess this is now