I know this is kind of a “general” direction, but I started with ribbon bars. Something like that could lead to ribbon racks, then eventually the medals themselves to define the racks. My first true collected medal was an Iron Cross 2nd class, 1914, purchased for $15 (in 1983). But I continued to focus on ribbon bars, assisted by my handy book Ribbons of Decorations and Medals by Guido Rosignoli, that I read through, page for page, about 50 times before I even turned 18. The book, published in 1977, is still all over the web in eBay and Amazon.