20 ÷ 3 = 6 R2
We're going to perform division on 20 with 3 as the divisor.

Step 1:
3 goes into 2 0 times with a remainder of 2.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 2 to get 2.
Bring next digit (0) of the dividend behind the 2 and repeat the process: 20 / 3

Step 2:
3 goes into 20 6 times with a remainder of 2.
Write down 6 as next digit of of the result. 
Result so far: 6
Subtract 18 from 20 to get 2.

The final result is 6 with a remainder of 2.