There are (I'd contend) four basic types of knot: Bends, hitches, bindings, and loops. Bends tie two cords together, hitches tie cords to objects, bindings wrap & grip objects together, and loops are loops.

You only really need one bend. I suggest the zeppelin bend, but they're all pretty similar. Hitches can benefit from a bit more variety, but a round-turn with two half-hitches will serve you well in most situations, along with its more secure variant, the anchor hitch. There's a trade-off between how secure a knot is and how easy it is to untie, which is why the less-secure variant is useful.

The best loop is the angler's loop, which will even hold in bungee cord. The alpine butterfly is also good to know because you can tie it "in the bight" (without access to either end of the rope), which is very handy.

Bindings are (I think) the most commonly-used family of knots for most people. Lashing a load into a truck so it won't move, tying a bag shut, and even tying shoes are all situations for bindings. For large loads, I'd suggest a trucker's hitch, which is good for (e.g.) tightly strapping a load into a truck bed, hence the name. For smaller situations, like cinching a bag shut, try the jam hitch—an underappreciated favourite of mine. It works like a zip tie, tightening around an object and not loosening. (Make sure the knot itself is tied tightly before you zip it. After you zip it, you can tie the ends together for extra security.)

Zeppelin bend: https://www.animatedknots.com/zeppelin-bend-knot

Anchor hitch: https://www.animatedknots.com/anchor-hitch-knot; round turn & two half-hitches: https://www.animatedknots.com/round-turn-two-half-hitches-kn...

Angler's loop (sometimes called "perfection loop"): https://www.animatedknots.com/perfection-loop-knot; alpine butterfly: https://www.animatedknots.com/alpine-butterfly-loop-knot.

Trucker's hitch (feat. alpine butterfly): https://www.youtube.com/shorts/o3BcaoPXK5Q; jam hitch (aka "rolling hitch zip tie" or "reverse midshipman's hitch"): https://www.reddit.com/r/knots/comments/12vsuk1/how_to_tie_a.... (Though these have "hitch" in the name, I'd argue they're better described as bindings, because they preserve tension.)

If nothing else, learn the round turn & two half hitches, the alpine butterfly, and the trucker's hitch. Some combination of these will serve you well in most situations.

One final tip, while I'm talking about knots. You may be tying your shoelaces wrong: https://www.fieggen.com/shoelace/grannyknot.htm.