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 city/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. I believe this means you need to show 800,000 Thai Baht in your bank account. This visa type will allow you to stay in Thailand for the whole 1 year (renewable) without going to the border or not leaving the Thailand anymore at all.