Coral World is a paid Aquarium attraction located next to the beach at Coki. They have their own web site so you can check it out.
Coral world itself is not a place for snorkelling. It is not a snorkel park.
On the beach at Coki there is some OK snorkelling. When facing the water on the right side (Coral World end) of the beach there will be loads of fish but not a lot of underwater color. On the far end (left side facing the water) there is some nice coral just offshore.
There are vendors who will take you on a beginners scuba dive to a nice coral reef located just offshore of the beach, probably a bit too deep for snorkelling.