By default Blogger shows your whole posts on your blog's homepage and archive pages. If you write long posts this can be a real pain because your blog's homepage will grow in height a lot and your readers will have to wait a lot for it to load and finally if they are patient enough to wait your homepage load fully they will have to scroll a lot to view your blog's content.
There are many tutorials over the Internet that advices you to deal with this problem by modifying your blog template's HTML code in order to show only the post titles on the homepage, but editing your blog's template can be a dangerous task, especially if you are not a web developer. It would be better if you could make blogger show only the titles and a short text for each blog post on your homepage and a "Read More" link that will expand the blog post when clicked. As a result your homepage will become smaller and more readable, it will need less scrolling and generally it will become more appealing to your readers. Fortunately, there's an easy way to do this now and you even don't have to edit your blog's template! All you have to do is to use the Jump Break button when editing your post to determine the place where Blogger should split your post and insert a "Read More" link.
Clicking this button will insert a gray line in your post but don't worry, it won't be visible in the post when published. It's shown only in the editor window to inform you where the "Read More" link will be inserted.
If you prefer editing your posts in HTML mode, you should insert the text <!--more--> in the place where you want the "Read More" link to appear.