43 ÷ 2 = 21 R1
We're going to perform division on 43 with 2 as the divisor.

Step 1:
2 goes into 4 2 times with a remainder of 0.
Write down 2 as next digit of of the result. 
Result so far: 2
Subtract 4 from 4 to get 0.
Bring next digit (3) of the dividend behind the 0 and repeat the process: 3 / 2

Step 2:
2 goes into 3 1 times with a remainder of 1.
Write down 1 as next digit of of the result. 
Result so far: 21
Subtract 2 from 3 to get 1.

The final result is 21 with a remainder of 1.