The first and second fundamental theorems of calculus are ordered differently by different people and textbooks.
But here they are.
In words, it means that you can evaluate an integral of a derivative from A to B by subtracting the value of the function at A from the value at B.
It also means that the derivative of an integral is the function. If the bound is a function of x (for example not from a to x but from a to x^2), then you have to times the function by the derivative.