Just, type your function (with the user friendly keyboard), and plot it.
You will see the result.
The user-friendly keyboard (in android devices allowing it), you will feel a vibration each time you press a touch
The button are well space, allowing a confortable typing (try it on a 240x320 screen and you will understand how cool it is)
Basic scientific functions (trigonometric, exp, log, ln, sqrt, and '+', '-', 'x', '/', and '^') are available.
Evaluating your function at x=0, is achieved by pressing the '=' button.
Plotting your function is as simple as pressing the 'plot' button.
When the function typed is not a valid expression, the function will be red colored.
When you want to observe a detail on the curve, simply move with your finger to the place you want to go.
If you want zoom in press the zoom-in button (right button on the bottom). Zoom out is achieved with the left button on the bottom.
finally you can get back to the (0,0) point by pressing the button between zoomin and zoomout