This CMOS IC can be directly connected to 7 common cathode segments (negative)

if you want to make 2 more digits, then we cascade / connect the level between ICs, so when the first IC reaches 5, the CO output will be Low (0) and when it reaches 0 will be High (1). 0-1 displacement will result in a counter added 1 so that the previous CO digit pin can be an input of CLOCK ic by further tens division

how about make 4 digit ?

Digit Up Counter circuit is when the Clock enters PIN 1 IC 1 on the unit counter then display 1 will display the number 0 then if we press the clock back display 1 will display number 1 and display 1 will continue to display numbers up to 9 and return to numbers 0 if we keep pressing the clock. This is all because when the 7 Segment Unit counts to 9 back to 0 then the Out Put of PIN 5 IC 1 triggers PIN 1 IC 2 counter Tens then Tens display will start counting from 1 to 9, then after Tens counts to 9 back to 0 then Out Put from PIN 5 IC 2 triggers PIN 1 IC 3 counter hundreds then Hundreds display will start counting from 1 to 9. After counter hundreds count to 9 and back to 0 then Out Put from PIN 5 IC 3 triggers PIN 1 IC 4 counter Thousands Thousands then Thousands display will count 1 to 9, after that return to the beginning of 0. PIN 15 on IC 4020 is as a RESET in arranging all the legs are all connected, when the 15 feet are connected to VCC (6-12V) then the Out Put counter will 0000 / Display 7 Segment will be 0. The function of the resistor in this circuit is as a waster or discharge is done so that the ripple that occurs is not too long. Polar capacitors in this circuit serve to smooth the ripple that occurs at the clock and reset. This is done so that the formed ripple can be refined. Then the function of Non-Polar capacitors is to filter the ripple or filter the ripple voltage on the IC and it will be discharged through the ground. This is done so that the ripple that occurs on the IC can be refined.