PADI Open water diver course
PADI Open water diver course is the most popular one in the world.
Basically, the course takes 3days. It has 3 parts: Knowledge development, Practice of diving skills in confined water(beach), then go to the Phi Phi islands diving spots for practicing (4types) by boat.
After the course, you will get a Certification Card. You can use it to dive up to 18m in all ocean in a lifetime.
PADI Advanced open water diver course
You will have more fun with diving. PADI has 24 types of adventure diving, if you complete five of them, you can be certified as an advanced open water diver. (deep diving and navigation diving are required.) Minimum of 2 days is available. Anyway you can do 13 types of the adventure diving in Phi Phi islands.
When you finish your PADI advanced open water diver course, you will get a new Certification Card, you can go down to 30m underwater.