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.