The More Block allows you to add a More Tag to your content. Most archive pages (e.g your blog page) only display a small excerpt of a Post and then provide you with a “Read more…” link to continue reading the rest of the article. When you insert a More Block into your content, everything prior to the tag is considered as this excerpt. Most times you’d only use this button when you’re creating a blog Post, rather than a Page.
You can only insert one More Block into each Page or Post.