It seems it would be very nice if a user could comment on or upvote something that just helped them solve a problem. I was disappointed that I couldn't enforce an answer or comment that really helped me because my reputation is so low. Seems silly, because some of the upvotes would probably be a lot greater if people doing searches could upvote them.
You can vote and comment once you have sufficient reputation. New users and those with low reputation cannot.
Here is what you can do as your reputation increases: https://stackoverflow.com/help/privileges.