The Music Professor site has lessons for sale on various instruments, and pertinent to TPA music classes, music theory.
There are two sample video lessons here , 1 ½ and 5 ½ minutes each, that I invite you to try. The one farther down the page has to do with key signatures for minor keys, a subject that mystifies some of my students. Sometimes hearing something explained a little differently is helpful.
If you find this site of benefit to you, please let me know.