The citizens of the following 19 countries, who travel to Hainan Province through international travel agency, are allowed to stay in Hainan without a China visa for 15 days. Indonesia is included. But the travel agency should be registered in Hainan and approved by China Tourism Bureau. You are Indonesian passport holder? If yes, you may join a travel agency and go to Haikou without a visa. But if you are an individual tourist, you need to apply for a visa.
Usually, on-site visa asks the applicant to prepare appointed photo, ID card, passport and the visa cost and so on. Besides, you should have the returning flight ticket (or the flight ticket to another country), the information of your hotel and the certification of your belongings. If you have an inviting letter, it would be better.