Click: Start > All Programs > Mathematics > Mathematica.
Once Mathematica is open, click: File > Palettes > Basic Input.
In the Palette that opens (or may already have been open), you will see various buttons, such as for square root, and definite or indefinite integrals:
You can click on and type inside each of the "input boxes" (or you can use Tab and Shift-Tab to jump between the boxes).
When done typing in the desired expressions, press Shift-Enter, or the Enter key that's on your keyboard's number-pad.
When you try to find a definite integral, Mathematica
usually gives you a long expression instead of just one number as the answer
(try it for the problem you're working on!). Here's what's happening:
Type in Sqrt[2] (or use the Basic Input palette) to find the square root of 2;
press Shift-Enter. Do this and see what happens!
What's the result? Mathematica doesn't give you
1.4142...; instead it gives you back what you typed in! Why? Because it
prefers to give you an exact answer. But you can tell it to give you
a numerical approximation by typing in N[Sqrt[2]] ; try it! N[ ] means "give me a
Numerical answer".
Note: capitalization and bracket-type matter: It's N[ ], not n[ ], nor N( ).
Now go back to the problem you were working on and put N[ ] around it and press Shift-Enter.