12 goes into 68 5 times, so put 5 on the top, and subtract 600 from 688. You will get 88 as your difference. 12 goes into 88 7 times, and since 12 times 7 is 84, put 84 under 88 and subtract it from 88. Your remainder will be 4.
Hope this helps!
(I have an example below)