Are you asking if you just have x, how do you get the antiderivative?
For something like 2x you would break it apart to 2∫xdx, which would then become 2 ∫ (xn+1/n+1)
so 2∫xdx would break down to 2 ∫ (x1+1/1+1)
2 ∫ (x2/2)
put it back together...
Are you familiar with anitderivatives? The derivative take you one way and the antiderivative take you the other way. This is what Ssnow is trying to show you.