Okay, so I looked it up. Apparently, you don't need to guess in proper Sudoku, when there is only one solution

Yup, you got it :)

, but apparently there are also many Sudoku, sometimes printed, which have more than one solution, and so you require guessing.

Yeah, but only where you have come to a place where a 50-50 guess is needed, when you get used to solving good puzzles you learn how to figure it out, and there is a lot of checkers that you can run on puzzles if you're not sure, and if you find one with multiple solutions you just evade that source.

Also There are known good sources for puzzles, ones that are proper puzzles, so the best choice is just to keep at them.

Also, some sites mention "guessing" as a technique, which I probably took it to mean that you have to do it.

Guessing is used in speedsolving, where they solve the puzzles really fast. Guessing is a valid technique in picross as well, you can just guess if a cell is filled or not, it's exactly the same in sudoku, you just cheat yourself, and it's a big likelihood that you made the puzzle unsolveable, personally I find it not very gratifying to guess, so I never do.

Since I believed guessing is required, I would leave the puzzle where I got a bit stuck, assuming this is where I need to guess.

Yeah, some of the techniques, like finned fishes, Alternate inference chains and 3d-Medusa and so on can get a bit involved, so if you haven't seen them before it's hard figure them out by yourself. I used to moderate the r/sudoku sub over at reddit, where we used to help people solve a lot of puzzles they were struggling with. But really difficult stuff like that usually aren't in printed puzzles, they seldomly have anything more complex than an X-wing.

If you want to learn about techinques https://hodoku.sourceforge.net/en/techniques.php is a really good source, and hodoku is a really good solver too in case you want to learn, if you want something online there is https://sudokuwiki.com which is decent as well :)

Thanks for the comment! If I start to like Sudoku again, the blame would be all on you! 😀

Hah, you're welcome, I've been solving for around a decade now, and it's still fun to me, so at least there is something for it.