The Day macro inserts the current day of the month.
The syntax for this macro is %[Day]
If the date is 10th April then the %[Day] macro inserts "10":
Figure 1. %[Day] Macro Example
Note that this macro is often used in conjunction with other macros in order to create combined output. For example the combined macros %[Time:H:mm] %[Month]/%[Day] output the current time followed by the month and the day of the month:
Figure 2. %[Day] Combined Macro Example