Big O Notation is how developers measure how fast an algorithm is. Don't be intimidated by these mathematical formulas. You can learn how Big O Notation works pretty quickly. (Though it will take some practice to understand it on an intiutive level.)
In his article, veteran teacher and web developer Beau Carnes explains Big O Notation using illustrations and a video. It should help you grasp the concepts much faster than just explaining them with text.
Read the full tutorial on freeCodeCamp's Medium publication (7 minute read).