Citizens from the United States, Canada, United Kingdom and many other countries only need a passport to enter Belize. No special VISA is required. When you arrive, Immigration will stamp your passport which allows you to stay here for 30 days. Each month you will need to go to an Immigration office for a new stamp to extend your stay. The first 6 months cost $50 BZ each time, after that it will cost $100 BZ.
After one year, you may apply to residency. Five years after that you may apply for a Belize passport and citizenship.