Measure Energy from Solar Panel

Hi Everyone! [Newbie Here software guy :)]

I need to measure the voltage, current from a solar panel [75Watts] which has an output of 18V max and I[max] being 6.

I went through the link below but I don't understand how to scale down 18V to less than 5V so as not to fry my arduino board.

Can someone explain which kind of resistors/circuit I need to use to measure such high volt and amps?