You have a very limited time within which to edit the post (for spelling errors, etc). Once the time has elapsed, as the members above have noted, you can no longer edit the post.

This is where you should go to read the guidelines for the Forums & for the Chat. It also has FAQ for the Chat, incl. how all the buttons & features of the Chat work. As for how the various & sundry buttons in the forums work... if you search through the Tech area, most of those questions have been asked & answered, or people are happy to help--just be specific with what you need (i.e. as you were with the "can I edit this post")--and don't post a whole laundry list of issues, and people will lend a helping hand...

As with most places, the more you browse around & utilize the various buttons & features, the more you will get to learn how they work. There is very little here that you can press & get into trouble with LOL...