Feed it a mouse or rat that’s equal to the thickest part of the snake. Never feed live unless you have to. That means after trying to feed it prekilled or frozen thawed for weeks and weeks and weeks and it won’t take it, then you may have to give it a live mouse. Other than that, either prekill the rodent, or buy frozen and thaw it out really good.

As for when to feed it...that depends on when you got the snake and when it last ate. Generally you feed it once a week. But if you just got the snake, give it atleast a week to settle in to it’s new environment(its cage), and don’t bother it at all. Just change water and spot clean if necessary. Then after a week, offer it a rodent. If it takes it, then good, you can give it two days to digest, then handle it a bit a few days after feeding it. Take it slow though...ball pythons are easily stressed.
If it doesn’t take the food item after giving it a week to adjust, then leave the snake be for another week and try again then.

As I posted in another topic of yours...read up on as many care sheets as possible, so you can keep this snake alive and not let it suffer or die. Sounds like you didn’t think this through and just got it as a surprise b-day present. Hope I’m wrong though.

Read these:

Alan Bosch Care Sheet
NERD Care Sheet
Kingsnake.com Care Sheet