How to enable expanded posts and why there is a "Read More!" at the bottom of every post now

When you click on Create Post and then Edit Html tab of Post Editor you will see the following

Replace the line "Here is the beginning of my post." (Type your summary here) with your summary paragraph. Then replace the line "And here is the rest of it." (Type rest of the post here.) with the rest of your post. Do not delete the other lines and . Also add your summary paragraph above both the lines and your rest of the post between the lines. Then click Publish to publish post.