Before we begin with the basics let's break down what a " transition " means. In case you don't already now transition is the motion that happens between two clips. Some of the most basic transitions that every editor learns in the very beginning are zooms, spins and slides. The rest is mostly based off of these 3 but there are also some more complicated transitions that require a little more advanced knowledge on the topic and good skills with the program you are using.
The basics of editing can be learned easily with the help of tutorials, here are some more popular tutorial channels on YouTube that provide useful tips and advices:
There are also a lot of Instagram accounts that offer help with any editing program, make preset packs and tutorials.
Now onto the basics. I'll list down some stuff that you'd need to know if you want to be an editor.