showing month in pivot tables

I have a worksheet that I use to keep up with the workorders at my work, the columns are "A" event number "B" date received "C" date completed "D" building name and "E" unit number I want to use a pivot table to track the number of work orders each unit gets in each month, when I put the date received and unit number in the pivot table it shows me each day of the month. How do I get it to show the workorders buy month only? I have tried making a new column "F" and putting in it =B1(date received) and copying it down and formatting it as MMMM this gives me the months January - December but the pivot table nonetheless shows it as January - December but as each day. I can type the months in column "F" that corresponds to the date received and the table will show the right numbers. How do I get the table to show the workorders by months based on what is in column "B"? Thanks in advance for your help.