You do this in the Visual Editor of the post where you wish to insert the button.

1) Look at the tool bar at the top of the page, and find the "Read More" button.

2) Make sure that you have a double space between the two paragraphs where you want the button to appear, as shown by the red arrow below. and put your cursor in the place where you want it, thus:

3) Click on the "Read More" icon, and a dotted line will appear between the two paragraphs.

4) Be sure to click on "Update" as soon as you have done that, and your post will then look like this in Editor mode:

You can then check your blog roll, and you will see that your post now has a line on it with the words "Continue Reading", thus:

Now you can do the same thing on all your posts, and voila, you have created a blog roll!

Next up..............

Conclusion