315 ÷ 8 = 39 R3
We're going to perform division on 315 with 8 as the divisor.

Step 1:
8 goes into 3 0 times with a remainder of 3.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 3 to get 3.
Bring next digit (1) of the dividend behind the 3 and repeat the process: 31 / 8

Step 2:
8 goes into 31 3 times with a remainder of 7.
Write down 3 as next digit of of the result. 
Result so far: 3
Subtract 24 from 31 to get 7.
Bring next digit (5) of the dividend behind the 7 and repeat the process: 75 / 8

Step 3:
8 goes into 75 9 times with a remainder of 3.
Write down 9 as next digit of of the result. 
Result so far: 39
Subtract 72 from 75 to get 3.

The final result is 39 with a remainder of 3.