How come I can't "grasp it?"
 

I watched Jenny Doan's tutorial on how to make mitered corners, however I'm using a rectangle(s), and Jenny Doan uses a square(s). How come I'm constantly finding out just how obtuse I really am. It just does not compute for me. Any help with how to miter corners on rectangles without the birthing method? Any OTHER tutorials to suggest I could watch?

Is this miter on binding or borders?

By far the best tutorial I've ever seen on mitered corners (and other finishes) is Bonnie Browning's class on AQS iquilt (https://www.iquilt.com/course/border...shing-touches/).

As far as a free online class, I'd go with this 4-part series by Sherri Driver of McCall's:
Joining the Strips https://www.youtube.com/watch?v=7Hha...&nohtml5=False
Sewing Binding to Quilt https://www.youtube.com/watch?v=X2MJ...&nohtml5=False
Joining the Ends https://www.youtube.com/watch?v=3w5n...&nohtml5=False
Turning & Hand Stitching https://www.youtube.com/watch?v=E6lv...&nohtml5=False

EDIT: If you liked Jenny Doan's tutorial except for the fact it was a square, the only difference between squares & rectangles is that to calculate the perimeter of a square, you measure one side & multiply by 4. For a rectangle, you add together the length & the width & multiply by 2. Everything else should be the same.

I have always done them the way EB explains doing them:
https://vimeo.com/27028498.

This is my favorite instructional video for mitered borders:

https://www.youtube.com/watch?v=mBVnUE2GMn8

I use EB method also. Works every time. Just don't trim until you re sure the miter looks good.

I can't see the difference between mitering corners on a rectangle or a square. Both have right angles at the corners. Am I missing something?

I demonstrate how I miter corners.

http://www.quiltingboard.com/attachm...w-tutorial.pdf

sandy

I leave the ends of the borders flapping, I fold one end in an angle, press the miter until it looks like I want it. I then glue it in place, then sew it. I don't measure or mark anything.

It doesn't matter what size/shape your quilt is, a mitered corner on your border or sashing is folded at 45 degrees, and is not changed because the quilt isn't a square.