You must enroll in a course from a school accredited by the Thailand Ministry of Education. The school will typically take care of everything for you, including sending in your application, communicating with the Ministry and resolving any issues that come up during the process. The Ministry usually takes 5-7 weeks to process applications, depending on your nationality and the volume of applications. After obtaining the acceptance letter, you can get the actual visa at Chaeng Watthana Government Complex in north Bangkok (we will meet you there to guide you).