To simplify your life I will give brief explanations:
L cancel - If you are in the middle of an aerial and you hit the gruond, there is lots of lag before you can do another action. By pressing L in the 7 frames (116ms) before touching the ground, this lag is halved, allowing you to do stuff quicker.
Wavedashing - Melee has directional airdodges. When you airdodge into the ground at an angle, you will scoot in that direction. So by jumping and air dodging diagonally down and left, you would scoot left. This isn't very useful for you because it's not very good on its own, you have to know how to apply it, which takes a bit.
Dashdancing is what Fox is doing in this gif to bait attacks from Peach.
TechingLedgehops - Dropping from the ledge and using your double jump to get back on.
You can also press R to roll from the ledge, A to attack from the ledge, or you can tap towards the stage with your stick to just get up off the ledge. There is no ledgeAnnoying Orangeing in Melee.