If you are writing a long post and you want to decide where the excerpt should end then you can use this button. Excerpts of your blog posts are shown on various parts of your site; such as the home page and archives.
Go to Posts → Add New and begin writing your post. Where you believe that your post is best cut; perhaps at the end of a paragraph or sentence… use the Insert Read More tag (keyboard shortcut; Alt+Shift+T). Continue writing your blog post underneath.
If you would like to change the link text ‘Read more…’, switch from the Visual tab (top right of the writing pane) to Text and look for this code <!–more >. To change the link add a space after <!–more–>, and add your own text – example below.
<!–more There’s more to read!–>