I wanna buy a new set of cranks for my dirt jump bike. However I don't know from which website to buy and if I do find some crank arms I don't know if they will fit my bike. I attached a picture of what my crank looks like.

Back when i had a bmx, it was way easier finding bmx parts online )

Any local shop to you should be able to help you out-failing that you might be able to get a new bottom bracket (I assume yours is a square taper crankset) you COULD go to a BMX setup fro cranks.

Looks like you need a crankset and sprocket. A pic of the bottom bracket shell will be more helpful, I can't identify that frame. Might be euro but some mtb/road bikes use other press fit stuff too. Also not sure on the width. Probably standard. Anyways yeah more pics.

I use albes.com (Michigan USA) empirebmx.com (Texas USA) and sourcebmx.com (Hastings UK)