To round 683.986 to the nearest hundredth, know your place values.
The first 6 is six 100s. The second number 8 is eight 10s. 3 is three 1s. 9 is nine tenths. The fifth number 8 is eight hundredths. The last number, 6 is six thousandths.
When rounding to the nearest hundredth, if the thousandth value is more than five thousandths, round it to the next place value, which is the hundredth.