First of all the calculator provides you various 2-D shapes in the drop-down on the 2-D shape. After choosing any one of them, you can perform your desired calculation.
The calculator asks you any input you want to pass as parameters. (make sure than you enter derired number of parameters). If the solution of the remaining parameters (the input fields that are left blank) is feasible by using the given existing values, the calculator will solve them step by step otherwise, the message will be displayed.
Make sure that you are entering the valid arguments. If you try and input the invalid arguments, the calculator will take the parameters those are encountered first and solve the rest of the parameters.