I just want to know what those numbers below the clock means in Windows Phone 8.1.
When I open the notification center, below the clock, next to the battery percentage, it says "5/6". Maybe it varies across different phones.
That's the current date. The exact format depends on your regional settings.
Looks like you're using US regional settings (month/day, no leading zeroes), as today is the 6th of May. On my phone it says "06/05" (UK settings, day/month).