I am a new to Tableau.
I appreciate you are new to Tableau.
A filter is applied to data to reduce the data based on the conditions of the filter(s). Therefore if I filter your data on November 2015, I only have November 2015 data, there is no 6 months before to display.
The reason parameters are used in place of filters is that they act outside of the filter, and therefore are not restricted by applied filters (all your data is still there, we can then choose what to display)
So in your example you would use a parameter with a logic test
The logic test acts as the filter, in place of a 'filter'
I can help you further, but you need to get this concept
to obtain this functionality you would need to use a parameter with a calculated field as your filter.
The calculated field would be something along the lines of:
if datetrunc('month',[Date])>Dateadd('month',-6,datetrunc('month',[Parameter Date Selection])) and [Date]<=Datetrunc('month',[Parameter Date Selection]) then '1' else '0' End
Place this field onto the filter shelf and then whichever date is selected in a given month in the parameter, the worksheet will show the selected month and 5 months prior.
As Mark has said, if you filter to November 15 data, all you have is 1 month of data so the best way to fix this is with the use of a paramer.
Hope that helps!