I'm not sure how much you already know, but you want to learn a mix of concrete endings, probably in the order of their frequency, and general endgame concepts to help guide you in other situations, such as king activity, opposition, fortresses, the awareness of the placement and general features of pawns, etc.
One strategy is to work through a single book. Although I haven't used it, lots of people like Silman's Complete Endgame Course, because unlike other books, the endgames are not grouped by the pieces involved, but chunked by rating, so you can slowly build up the most essential skills. Or you could use 100 Endgames You Must Know by de la Villa, in which case you could find his list in the introduction of the 20 or so most important endings and learn those first, and then move through the rest of the book.
You could also find a list of how often the various endings occur and learn them one-by-one, either by looking at relevant book chapters or finding studies here or even good videos. Whichever approach you take, I would strongly recommend that you make studies out of them here for yourself, because taking notes like really helps you pay attention. Once you learn a new idea, you can use the practice section to drill yourself over and over, or just set up a position on the board and play against the computer.
Because the endgame is heavily focused on pawn promotion, you definitely want to learn all the basics of king and pawn vs. king endgames, because often your goal will be to reduce to a favorable version of that ending, or prevent your opponent from doing so. In terms of pieces, rook endgames are the most common and also have a lot of material to cover, so you want to know some basics of those early on.
There's an excellent book called Secrets of Pawn Endings by Lamprecht and Mueller. I read it probably sooner than most people would recommend by rating, but it was a revelation for me. Not only did I feel like I understand how pawns work in the endgame, but I felt like I understood middle game structures better and how to liquidate more effectively into an ending, and even started to see openings differently.
I have some endgame studies with exercises if you want to browse through them and there are many other great studies here as well. You probably want to read a book chapter on this, but here's one on king and pawn vs. king with some basics of critical squares and opposition with exercises to practice: