Step 1:
Enter the function into Y1=.
Arrow down so the cursor is in the
Y2= entry space.

Step 2:
GRAPH the original function to
see that your viewing window gives a good representation of the graph. 
Step 3:
We will be using the nDeriv
command found under the MATH key.
Hit the MATH key and arrow down to
choice #8 nDeriv(.

Step 4:
The nDeriv command will appear in
the Y2= entry space, where you
left the cursor.
We will be using the parameters
nDeriv(Y1, X, X).

Step 5:
Hit GRAPH. 
Step 6:
To more clearly distinguish the derivative graph, set the
graph style to a thicker line (or graph the derivative separately). 