Underlying any language teaching approach is a theoretical view of what language is, and of how it can be learnt. An approach gives rise to methods, the way of teaching something, which use classroom activities or techniques to help learners learn.
Example
The communicative approach is the best-known current approach to language teaching. Task-based teaching is a methodology associated with it. Other approaches include the cognitive-code approach, and the aural-oral approach (audiolingual method).
In the classroom
Learners in the modern language classroom often learn through techniques drawn from a variety of methods/approaches in what has been labelled an ‘eclectic approach'. Teachers select techniques from various approaches according to the different needs of their learners. Most coursebooks mix methods and techniques in this way.
Further links:
https://www.teachingenglish.org.uk/blogs/james-taylor/james-taylor-ppp-ttt-tbl-dogme