This video seems to make it more difficult than necessary but it is probably doing that on purpose.
If you get your head around difficult terminology it usually means you are learning properly, hopefully at a deeper level.

A better graph representation:

\(\displaystyle \lim _{x\rightarrow 0}\;f(g(x))\\ \text{I would just have said that } g(0)=2 \;\;so\;\;\\ =\displaystyle \lim _{x\rightarrow 0}\;f(2)\\ =0\)
Let's see what the video teacher was saying
\(\displaystyle \lim _{x\rightarrow 0}\;f(g(x))\\ \)
Look at the g graph first.
I am just referring to red stuff that he talked about. He has not explained it well.
look at g function first (vertical axis is g, horizontal axis is x)
As x approaches 0 from the negative x side (he has called the left side the below side.)
g approaches 2 from higher g values,... from above
Now move over to the f function
If you are going to find f(g(x)) then the horizontal axis become g(x) or g NOT x and the vertical axis is f(g(x)) or just f for short.
So g is approaching 2 from above means that on the f graph, g is approaching 2 from the right side.
See if you can get your head around that.

LaTex
\displaystyle \lim _{x\rightarrow 0}\;f(g(x))\\
\text{I would just have said that } g(0)=2 \;\;so\;\;\\
=\displaystyle \lim _{x\rightarrow 0}\;f(2)\\
=0