First you have a typo in your problem.

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.