Did you know that when you use free-form input to enter calculations into Mathematica, it can often guide you step by step through the process of solving many of these problems? After evaluating the free-form input, click on the plus sign to the right of the input ("Show all results"), then click "Show steps".
Here are just a few examples of mathematical problems that show step-by-step solutions.
solve 3x^2 + x-7 = 4 x
limit of x^x as x -> 0
derivative of (3x^2+1)/(6x^3+4x)
integrate e^2 x cos(3x)