Lets start by pointing out that karate isnt just ONE form of martial art. There are thousands of very different styles! literally! From JKA (Japan Karate Association) and Shukokai to Inoue-ha (my style!). All of which are created or moulded from a variety of backgrounds and therefore some are almost uncomparable. They all have their own world champions and obviously all believed that their styles, were the way to go!
So now they have created an "all styles" semi-contact curcuit where all the styles can compete together. Each competitor falls under one of the 4 general style groups; Shotokan, Goju-ryu, Wado-ryu and Shito-ryu. (thats mine!). And every referee should be able to ref these general groups of styles!
Now that we have established that..the question arises." But what DO you guys to?"
There are 2 things...
1st, its the 'fighting' called kumite. (pronounce it like..koom-it-ay) This is where we where super light gi's (those white karate suits we all wear) and try to score points on eachother. 1 point for a punch to the head (no contact!) or to the chest. 2 points for a kick to the side. and 3 points (this is a big deal) for a kick to the head or a take down! The person with the most points at the end of the time limit, wins! Its that simple!
Here is a super cool selection of kumite fighting best moments(3 pointers!) that just gets me so excited!
Secondly, there is KATA! Now this is a sequence of karate movements that are practised to show to the referees at a tournament. One has to know at least 7 different sequences! Each competitor will perform they kata and the the refs, using a red or blue flags, decide who they thought did the best one! I really love this one!
Here is an example of the current world kata champion (the legend, Antonio Diaz!) doing a kata called Annan.
And thats it! Hope this quicky overview of what competition karate is sheds some light on the matter.
If i havent clarified anything enough just pop a question in my comments box!