99 ÷ 5 = 19 R4
We're going to perform division on 99 with 5 as the divisor.

Step 1:
5 goes into 9 1 times with a remainder of 4.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 5 from 9 to get 4.
Bring next digit (9) of the dividend behind the 4 and repeat the process: 49 / 5

Step 2:
5 goes into 49 9 times with a remainder of 4.
Write down 9 as next digit of of the result. 
Result so far: 19
Subtract 45 from 49 to get 4.

The final result is 19 with a remainder of 4.