Here is an example program showing the use of some of the calendar time functions.
#include <time.h>
#include <stdio.h>
int
main (void)
{
  /* This buffer is big enough that the strftime calls
     below cannot possibly exhaust it. */
  char buf[256];
  /* Get the current time. */
  time_t curtime = time (NULL);
  /* Convert it to local time representation. */
  struct tm *lt = localtime (&curtime);
  if (!lt)
    return 1;
  /* Print the date and time in a simple format
     that is independent of locale. */
  strftime (buf, sizeof buf, "%Y-%m-%d %H:%M:%S", lt);
  puts (buf);
  /* Print it in a nicer English format. */
  strftime (buf, sizeof buf, "Today is %A, %B %d.", lt);
  puts (buf);
  strftime (buf, sizeof buf, "The time is %I:%M %p.", lt);
  puts (buf);
  return 0;
}
It produces output like this:
2024-06-09 13:50:06 Today is Sunday, June 09. The time is 01:50 PM.