Old Dude Needs New Trick

I find myself drifting around in the blogosphere, admiring all them wild and professional kept blogs, and have come to notice that some bloggers list their earlier posts under categories, and guess what this old dude wants to know is----how they do that? Whats the trick to that trick? Kinda suspect it has something to do with tags, or labels and awww jeez haven't quite figured out all that---" things that go bump in the night" stuff ----yet. Anyway---- somebody wanna try to teach this old dude the trick of cross referencing my blog posts under categories?