Does anyone here know a good school on where I can study a course to like TEFL for me to teach English in Thailand?
I am going to assume that you do not hold Thai citizenship, and that you want to teach in Thailand legally, since not doing so can have serious consequences.
In order to legally teach English as a foreigner in Thailand, you need to get a Teaching Licence and a Work Permit. A teaching licence requires you to have a bachelor's degree.
A Work Permit in Thailand is tied to a specific job, at a specific location. This is usually not a problem if you work as a teacher, as you will be teaching for one school at one location.
If you do not earn more than a specified amount (varies depending on your nationality - but usually between 40,000 and 65,000 THB per month) then you will not be able to get yearly extensions of stay based on employment. This means that every time you enter Thailand you will get an entry stamp giving you 90 days before you have to leave. You can leave then come immediately back and get another 90 days, but still need to do this border run every 90 days.
If you DO earn more than the threshold amount for your nationality, then you would qualify for annual extensions, and would not need to leave Thailand during that year. These can be done indefinitely, as long as you keep renewing the Work Permit every year, and get the annual extensions of stay. If you do intend to leave (e.g. to go on holiday) you would need to get a re-entry permit when you get your extension, otherwise you would need to start all over again as soon as you leave the country.
Office workers and teachers in larger schools have all the paperwork done for them by their employer.
If you do find a school willing to employ a foreigner, make sure that they are prepared to provide you with a Work Permit. Otherwise you would be working illegally, and could be deported, fined, and possibly even blacklisted from entering ever again. Some less scrupulous schools will claim that you don't need a WP, but they are lying - everyone working in Thailand (even voluntary work, as highlighted in the aftermath of the 2004 tsunami) requires a Work Permit in order to do so legally.