Here are the various types of Visas for Thailand as of August 2017. *Please note that you should always check with the Thai Embassy in your country for updated information.
Visa on Arrival
This is when you arrive in Thailand without a visa, but you are from one of the 52 countries that Thailand allows to enter without prior documentation (this includes UK, USA, CANADA and most of Europe). You will get a stamp in your passport when you arrive and can stay for 30 days. There is no payment required.
Visas you need to apply for outside of Thailand.
This is a 60-day Tourist Visa to Thailand that can either be a multiple or single entry and can be extended for up to another 30 days by means of a visa run. If you want to extend longer than 30 days, you can convert the visa to a Non-Immigrant Visa which will require you to go to the nearby city or country such us Penang and Kuala Lumpur, Malaysia.
This is normally a single entry visa to Thailand valid for 90 days. Like the tourist visa, you can extend your stay by doing visa run going to the border or nearby country.
If you want a Retirement Visa in Thailand, you need to be 50 years old or above and meet the special financial requirements for the application. At time of this article a foreigner must show evidence of 800,000 Thai Baht in a bank account for at least 3 months. This visa type will allow you to stay in Thailand for the whole 12 months (renewable) without having to leave the country.