Take advantage of the lessons that are available on this website. They're quick, easy to follow, and have examples to do yourself after each lesson.
https://www.chess.com/lessons/winning-the-game
Checkmating
Bobby Fischer Teaches Chess is pretty much entirely about finding ways to checkmate. I would say that's helped me improve my end game the most. Don't get the book used though, as the entire point of the book is you writing the answers to the problems on the pages, and the book wouldn't be all that helpful for you if you're just staring at the answers that someone else has already filled in.

I don't like the lessons because I don't have a membership, and I do 1 lesson then can't do any more for the WEEK, it's sort of ironic how chess.com only let's you have unlimited lessons for 100$ a year, because the reason people want a membership is for lessons, so chess.com makes it expensive which I don't think is worth it, I can get lessons in a book for 80$ less.
I don't like the lessons because I don't have a membership, and I do 1 lesson then can't do any more for the WEEK, it's sort of ironic how chess.com only let's you have unlimited lessons for 100$ a year, because the reason people want a membership is for lessons, so chess.com makes it expensive which I don't think is worth it, I can get lessons in a book for 80$ less.
They give you a free trial of a week, and then you can do a month of diamond status (unlimited lessons) for $13. You should be able to go through quite a few lessons (or all) in that time, then use a cheaper level subscription to just do a couple lessons a week when you want a refresher.
I do not know how to checkmate somebody.