My friend just started being a Vegetarian but I dont know much about it.
It is the practice of abstaining from the consumption of meat. Some may go as far as to abstain from any animal slaughter by-product.
That seems really difficult. Can they eat fish?
Some vegetarians do still eat fish or seafood and some avoid it.
I see. So there is different levels almost of being a vegetarian.
The practice can be adopted for many different reasons. It just depends on each individual person.
Are there special vegetarian restaurants? 
Yes there are some and they are starting to gain popularity.
Do people around the world practice vegetarianism?
I am not sure where all it is practiced.