How do I write the code?

Have your arduino get the date(mm/dd/yyyy) & time(hh/mm/ss) from the user via the serial monitor in the arduino software.

Date includes day, month and year

Time includes hour, minutes and seconds

You circuit/program should:

print a prompt on the serial monitor,

get input of date and time from user

display date and time on the 16x2 display

keep accurate time on 16x2 display

include error checking for input that doesn't make sense (hours not in range of 0 to 23, minutes not in range 0 to 59, month not range of 1 to 12, etc).