Modify Theme’s Post layout?

I can’t seem to find the correct way to modify the look of my Theme’s Posts?

Right now a post looks like this:

Post Title
Posted By on Date / Category / Comment
Post Content

and I want it to look like this:

Post Title
Date
Content
Comment
(No CATEGORIES section in post)

Am I supposed to modfify the stylesheet and different template pages? I can’t find any ‘post’ info on my stylesheet and there is no ‘post’ template page either and when I look through the different template pages I can’t find anything that looks like the post content? I’ve been going through all of the Codec docs and can’t seem to find a solution.