Navigation Bar

http://wordpress.org/support/topic/277681
Hello. How do I create a navigation bar, like ones I see on so many sites? I’d need it for my posts, not the pages. The bottom line is that I have posts each of which describe a Roman coin. I’d like a navigation bar that would list all the emperors represented, so the visitor would click on the name and it would bring up all the coins (posts) under that name. Rather like the search engine does, which works great, but the visitor has to know which emperor to enter in already. Sorry for the longwindedness. This would have to be something very simple. I’m very, very basic with computers. Thanks. Kim