You would simply do 8 over 20 or 8/20. Think of the fraction symbol as the phrase "out of". 8 out of 20 counters are yellow. To simplify, you find a number you can divide both 8 and 2 by. You can either divide it by the 1st number you know you can (such as 2, but then you may have to divide it multiple times to get it to the simplest form) or find the highest factor to divide by (such as 4). 8 divided by 4 is 2 and 20 divided by 4 is 5. So your answer in simplest form is 2/5.
