Maybe one day I'll get around to writing versions of rules to puzzles with a nice tutorial element to them.
However, a pretty good version exists already
, courtesy of nikoli. See below for direct links.
Another great source is courtesy of the Grandmaster Puzzles blog, The Art of Puzzles
. That said, finding the rules to puzzles is a bit harder work there. You'll typically have to find a post with that puzzle first, and then on it will be a link to the rules. I'm not going to do that for you.
Up until August 2020, I published puzzles under an easy / medium / hard rating system.
Currently, I am using a 10 point scale to grade difficulty, roughly calibrated to these descriptions. Please note that your experience may vary from these ratings, as they generally penalise solving techniques that use uniqueness, bifurcation or intuition/visualisation.
[1, 2, 3] - (Very) Easy
These are beginner friendly puzzles, possibly with a smaller than usual grid size.
[4, 5] - Medium
Puzzles that require the solver to have at least some experience with the puzzle in question and may require a bit of fresh thinking to solve. You might see this kind of thing at the easier end of a puzzle competition.
[6, 7] - Hard
Puzzles that require lots of experience with the puzzle in question, and might have a tricky break-in, require novel/rare solving techniques, or have a particularly narrow solving path. They might also have a larger than usual grid size. You might see this kind of thing at the mid range of a puzzle competition.
[8, 9] - Very Hard
Puzzles that give experienced solvers some trouble. Everything I've said about a "Hard" puzzle applies here, but generally turned up a notch throughout the solve. You might see this kind of thing as one of the hardest offerings of a puzzle competition.
 - Extra Hard
Puzzles that push even the most experienced solvers to their limits, and may take a considerable time to solve. I would not include such puzzles in any puzzle competition that I might be responsible for.
I also reserve the right to turn things up to 11 on an exceptional basis. Although you probably won't see too much of 10 to be honest.