There are two editing fields. First one is destined for function  y=f(x) editing, second one for is destined for the derivation y'=f'(x) of the function editing. You can switch the fields using "Function editing" and "Derivation editing" options. Press the "Ready" button aftrer formulas entering. Then you can see diagnosis Correct/Incorrect. There are following rules for formula editing. Click mouse on a necessary symbol. Then drag symbol to necessary place. Click mouse once again after gray cursor appearing. Double click sets the symbol behind former set symbol. If you set exponent then drag symbol to the right top of  base. If you set the logarithm base then drag then drag to the right bottom. If you want to delete symbol then set the mouse cursor on it and click the mouse after gray cursor appearing. You can use a school formula notation. For example the  sinx , cos2x are accepted.