Day Function:-The Day function will Returns the day of the Date and Number of the day for that month

Example:-

a=Day(01)
msgbox a
Output=31 (Number of Days)

b=Day("01/May/2014")
msgbox b
Output =1 (Return the Day)

c=Day("01/May")
msgbox c
Output=1 (Return the Day)

a=Day(Date)
msgbox a
Output=21 (Return the current date of the current month as per system date)