The circuit is based around the 4017 counter IC. It is a CMOS type and can work from a wide voltage range. The circuit shown will count input pulses at the clock.
The outputs can only drive a few mA so unless connecting to other logic devices, you will need a driver.
Leave inputs as they are if not using them.
It is a digital device and works with logic level inputs. A high refers to +v and low refers to 0v.