Most people don’t need to be certified to go diving in Costa Rica. If you are not certified you need to take the course that the diving tour operator will give you. Generally there is a video, and sometimes verbal and written courses depending on where you go. You will also usually spent a little time in the pool. The entire course takes about 2 hours. Once you complete your scuba diving course in Costa Rica, you’re ready to dive.
For those interested in getting certified, you can do that in Costa Rica as well. You will be required to take what is usually a 3-day course, and is done by the company who you are diving with.