the best way to find things that you may not have made a comment on is to use Advanced Search. when you get there, you will see two tabs. i get the best results when i use the left tab. if there's something that you know you will want to come back to later, you can use the thread tools to get back to it.
as far as where to post, click on the Home tab. it lists all of the forums and a description of what goes in each forum. it also helps to be familiar with the Community Guidelines and the guideline for the individual forums. these can be found by clicking on the forum and looking at the first sticky thread.
hope this helps