The only stupid question is the one that isn't asked. We all started somewhere...WELCOME!

I, like many, use the 10%-15% 1x/week rule. The meal should be approximately 10%-15% of your snake's body weight. I would recommend getting a scale that reads in grams. You can pick these up at most office supply stores, WalMart, or order a decent one from Reptile Basics. I weigh mine the day before feeding (Saturday) and feed on Sunday. As to the "sizes", this is a decent chart I have used over the years. It gives you mice and rat sizes and the interchangeability of the two. BPs can live on mice alone just fine, but I find rats to be more filling and strictly feed F/T rats: