Exponential functions are patterns that get continuously multiplied by some number. It's exponential growth when the base of our exponential is bigger than 1, which means those numbers get bigger. It's exponential decay when the base of our exponential is in between 1 and 0 and those numbers get smaller.
A simple example is the function f(x)=2x. is an example of exponential decay. It gets rapidly smaller as x increases, as illustrated by its graph. In the exponential growth of f(x), the function doubles every time you add one to its input x.
The initial value can be considered the y-intercept for a linear function. It can be found by substituting 0 in for x and solving for y. This will give the initial value.