Explanation
The MONTH function takes just one argument, the date from which to extract the month. In the example shown, the formula is:
=MONTH(B4)
where B4 contains the date January 5, 2016. The MONTH function returns the number 1 representing the month( January) of the date. Note that you can use MONTH to extract the month from a day entered as text:
=MONTH("1/5/2016")
However, using text for dates can produce unpredictable results on computers using different regional date settings. It's better (and more flexible) to supply an address to a cell that already contains a valid date.
Get month name
To extract the month name from a date, you can use the TEXT function, as described in this example.