Depending on the show there is usally 7 judges.
Lets say this certain class had 5 people in it. The judges will rank them 1st to 5th by muscularity, definition and symmetry. So lets say it like this:
Judge1 Judge2 Judge3 Judge4 Judge5 Judge6 Judge7
2........1........3........1........1........2.... ....2
Then they drop the highest (3) and lowest score(1) so his scores will be 9 points all together.
The person with the most lowest wins.