If you have a lot of posts in your blog, you may want to have only excerpts on your homepage that link to the full blog post. Compare these two blogs (which both have some great content). And He Blogs and Professor Josh. Which one is easier to quickly scan through? Hopefully you choose the latter 🙂
To make short excerpts on your homepage, click on the “Insert More Tag” toolbar item when creating or editing an entry. Doing so cuts off the content where your cursor is at. Ideally you’ll want to have a nice intro paragraph that would be featured on the homepage, then more content you click on the link.