I don't understand the numbering system for the flex, flex-grow etc

In this video Guil uses some numbers on the flex and the flex-grow property. He used the flex-grow on the .nav element and he gave it a value of 1. Since he didn't mention what the numbers stand for or anything, I experimented with other numbers, whole numbers decimal numbers, but none had any effect, except the number 1. Why is that? Then he used the flex property but he used it on the .col element. I notice it does something similar to the flex-grow property so I tried it on the .nav element and it had the same effect as the flex-grow. on the .col element he used numbers 2 and 3 and they changed the sized of the columns, however when I used flex on the .nav element it still only changes with the number 1, but on .col it changes and gets bigger when you use 2 or 3, but when I tried to use 4 to see what results it would have again, nothing happened. So it seems weird to me that a certain range of numbers work and others don't and where that same range works on the .col, it won't work on the .nav. Please can someone clarify that for me. And please I'm a newb so speak clearly and in layman's term please. thank you guys.

Guil Hernandez