Math help

specifically, integral calculus help

specifically^specifically u-substitution.

I just don't get it. At all. My teacher's have tried to explain it, but I still don't get it.

So, do any of you guys get it? Do you have a tool or trick for doing it, or was it just memorization? Do you have a fandom reference?

I just really need to understand this concept, and for some reason it doesn't make any sense to me so far. =_=;