In QlikView, many times we need to create a calendar reference object which can be linked to any data set present in QlikView's memory. For example you have a table that captures the sales amount and sales date but does not store the weekday or quarter which corresponds to that date. In such scenario we create a master calendar which will supply the additional date fields like Quarter, Day etc as required by any data set.
In that case, you will find 100s of blogs and questions related to master calendar, fiscal calendar, canonical calendar etc.
try to spend some time on community search and let us know if you don't know some specific blog or question/answer.