I m 13, and whenever I try and go really high my voice just cuts off, why is that??

That your voice cuts off when you want to sing a high note means that the high note is not within your vocal range

Because you're attempting to sing above your vocal range. You obviously do not know how to use your voice.

technique is important

If You are a boy your voice could be changing and if You are a girl You may need to sing Alto. I have been singing all my life and I have never had a Soprano voice or a higher range so I learned to sing Alto, a lower range.

Puberty. It happens to everyone :)
A way to avoid your voice cutting out is to practice everyday and go freestyle. It should sound bad at first but it will help you become a better singer now and especially in the future. I started singing when I was in fourth grade and I'm now in sixth. I can tell I am becoming a singer, but I still need work.

Your vocal cords are like a rubber band. the more power you use In your voice, the more stretched out your vocal cords get. You want to get more powerful little by little. Its one of those things you just cant give up on. And its not about talent, its about pride and bravery.

Good luck!!

cuz u arent meant for that pitch. soz bro

Use gargale with some boil water and honey.