There are many ways to learn how to make a Stirling engine. If you want to just get going and make your first DIY Stirling engine and you don’t care about looks or precision (I mean machine shop precision) then I would suggest some of Jim R. Larsen’s books.
I have also read and would recommend books by James R. Senft. His books are a great for learning and understanding how Stirling engines work. If you read his books (usually under 100 pages) and apply your new understanding to your first Stirling project you will most likely have success.
If you want to learn how to make a Stirling engine you can find inspiration and instruction on the internet. There are many web sites that have fun tutorials like Scrap to Power. You can also find many videos on Youtube that will give a great start. I will have a homemade Stirling engine video gallery put up soon.
Here are a few resources that I have found that I think will help you learn how to make a Stirling engine. Some of these sites have plans Solarheatbuilder.com has a great engine design that is buildable without the aid of a lathe or milling machine.
If you choose to build the Quick and Easy Stirling engine by Jim R. Larsen it will not be difficult at all. I read his book in one evening and started working on my first engine the next evening. It was cheap too. I think the total out of pocket was about $5.00 after a trip to the local dollar store. This is a great place to begin. The difficulty of build only increases. My next few projects will most likely be from his other books. Jim has a few Low Temperature Differential Stirling engines that I’d like to try to build. Although, LTD Stirling engines take a little more precision and are a bit more difficult to build.