Navigate to Wolfram|Alpha in a web browser. Type the word "plot," then your derivative equation in the box in the center of the page. You may need to convert the equation to symbols a computer can understand, though Wolfram|Alpha is smart enough to understand many notational variations. For example, "plot f(x) = sin(0.2 * x^2)" uses an asterisk for multiplication and a caret to indicate a superscript.
Push the "Enter" or "Return" button on your keyboard.
Double-check the "Input" field on the resulting page to make sure Wolfram|Alpha's interpretation of your equation is correct. The graph of the slope field will be directly beneath, usually with two different scales to choose from.
Hover over the lower left corner of the "plot" box to see an option to save the graph as an image file or export it as text.