Second we are not mind readers so please tell us that the function is the Cumulative distribution function
Cumulative distribution function - Wikipedia, the free encyclopedia
Your book or the above wiki will tell you that the CDF is the integral of the PDF
So to undo an integral we will use the fundamental theorem of calculus to take the derivative of
This will give the PDF
This will answer the rest of you question.
Exponential distribution - Wikipedia, the free encyclopedia
If you get stuck please post some work so we can see where.