entries for members only and members registration?

Hi, I’m wondering how I can only allow registered users to read my entries, and how I can allow persons register on my blog, I want that when someone enter to my blog, only appears a post with the normal theme that says that they need to register and a link somewhere that allow them register, and after they register, they can read my entries, but not post or modify anything, is that possible? how I can do it? I’m sorry if my english has mistakes and thanks any reply