Online TEFL courses have do not usually offer teaching practice with real students and detailed feedback.
Weekend or ‘taster’ courses may giveg you an idea of what to expect when teaching English as a foreign language. However, you will not get the full range of input ‒ training in teaching methodology, language analysis, classroom management, and so on ‒ that you will get on a longer course.
More importantly, it is not a recognised qualification and no quality school would accept you as a qualified teacher.