YouTube is a good tool if your teacher is bad which is good that you are using. Does your teacher have tutoring? Even if your teacher is bad, if you can get him with you in tutoring, it is typically more favorable conditions as there are less people and it's easier to ask questions. If you can even get 1 on 1 with your teacher, I think it would be easy for him or her to explain to you even if he or she is bad at teaching.
Azarah is right in that for f(g(x)) you just plug in the g(x) equation into the values for x of f(x). I can't tell exactly what your questions are so here's an example:
F(x)=x^2
G(x) = x 3
F(g(x))=(x 3)^2
And a slightly more complicated problem:
F(x)=3x 6 x^2
G(x)=5x-4
Now plug in (5x-4) for all x values in f(x).
F(g(x))= 3(5x-4) 6 (5x-4)^2
If the question was to find g(f(x)) then you plug in f(x) for all of the x values in g(x)
G(f(x))=5(3x 6 x^2)-4
This is confusing to understand initially but once you get the hang of it, it's quite simple
I remember doing this 6 years ago and it is very useful to understand this.
