Look at the exponential expression:

the number "5" is the base and the number "4" is the exponent

What this means is 5∙5∙5∙5.  This is equal to 625.

We take the base and multiply it by itself 4 times!

Take a look at 3∙3∙3∙3∙3∙3∙3

Another way to write this is:

which is equal to 2187.

So let's go a little further. 
What do negative exponents mean?

Take the exponential expression:

This can be re-written as the reciprocal of

, which is

So the expression is equal to .

Let's look at some practice problems.