The methodology section should contain all of the steps you used to collect your data, invariably called as research methods for dissertation. Should provide enough detail so someone could replicate the process exactly.
Action dissertation research method (people try to improve their strategies in order to find the solution of the problem);
Classification dissertation research method (people recognize the object, try to understand and to differentiate them);
Experience dissertation research method (people try to find the solution of the problem being guided by their intuition and experience);
Experimental dissertation research method (people test their hypothesis by taking a practical test);
Participant observation (people observe the actions and the reactions of some individuals or group of people);
Statistical analysis (people collect the data, analyze it and explain it).
Make a list of all the disadvantages of the other methods for dissertation compared to the one you have chosen and then write down why you chose your method over those ones. e.g. chose snowball sampling because it allowed me to gather information quickly whereas if I had used strata sampling it would have been more time consuming.
Oh gosh. I first read this title and thought you were a grad student asking how to do this on a forum and felt a little freaked out for you. Good luck with how you are dissemenating this knowledge resource to those that are not familiar.