It covers all the essential knowledge and tools needed to teach English overseas.

I highly recommend World TESOL Academy's certification course for those who desire to teach overseas.

The 120-Hour course is the complete package: It covers all the necessary knowledge required to teach English, has a plethora of great examples and exercises, and provides effective tips for teaching students of all ages.

For those experienced in the language, the entire program can be finished in an accelerated manner.
Make sure to check out the supplementary links the developers provide as many of them provide deeper insight into the subject discussed in the chapter.

Overall it is a great program and I would recommend it to anyone who wishes to know the ins-and-outs of the art of teaching English.