Reddit mentions of Essential Chess Endings: The Tournament Player's Guide

There are many different kinds of endgames. King and pawn endings are the most basic. I guess rook endings is the next step above that.

I learned practical endings from this book which looks like it's out of print now, unfortunately. Silman has a book that's also supposed to be very good.

There are also specific books that dig into very particular aspects of endgame play, like this book on pawn endings that heavily focuses on "corresponding squares". That book helped me a lot.

For practice, I found this android app to be very helpful. I believe there is also a PC version and probably an iOS version as well.

Playing endings out against a computer can be helpful but there are big downsides, too. The computer will usually not find the most stubborn human defense, for example. If a position is objectively lost it will just play any trash move because it sees everything as equally losing.

In addition to all of this, there's always the psychological aspect of chess -- meaning, it helps to keep in mind what you're actually trying to accomplish and to learn mental tricks to make playing endings easier. For example, sometimes it helps to imagine rearranging the pieces or pawns into a winning position and then figuring out how to work backwards from that. Also, it helps to keep in mind that zugzwang is a common factor in endings. When you're trying to checkmate somebody, it helps to visualize a mating "net" around the king, like imagining the squares he can't move to as being highlighted. There are also specific tactics and patterns that come up over and over again in endings.

It's a big subject!