Use in a text box expression over a column(s) of related data you want grouped together.
If you want the text to change based on a parameter called AsOfDate, that will show the last full month month name and year. Use this formula in the expression.
=MonthName(Month(DateAdd("M",-1,Parameters!AsOfDate.Value)))& " "& (Year(DateAdd("Y",-1,Parameters!AsOfDate.Value)))
for example if the AsofDate = 10/15/2010
the expression returns
In SSRS you must format the Text Box to be Number - Date - January, 2000