Post thumbnails

Hi – I’m trying to get thumbnails for my posts to appear on the home page list of recent posts. Every time I set a “featured image” on a post, I get stuck with the same size image for both the post page and the home page (thumbnail). That means, they either both have a thumbnail sized image or they both have a large sized image. I honestly prefer to add pictures to the post itself (so I can pick where in the post it appears and how). But then, the image doesn’t show up on the homepage as a thumbnail. How can I make this happen?