90 ÷ 2 = 45 R0
We're going to perform division on 90 with 2 as the divisor.

Step 1:
2 goes into 9 4 times with a remainder of 1.
Write down 4 as next digit of of the result. 
Result so far: 4
Subtract 8 from 9 to get 1.
Bring next digit (0) of the dividend behind the 1 and repeat the process: 10 / 2

Step 2:
2 goes into 10 5 times with a remainder of 0.
Write down 5 as next digit of of the result. 
Result so far: 45
Subtract 10 from 10 to get 0.

The final result is 45 with a remainder of 0.