When does puberty occur? What causes the changes that occur during puberty?

Around when you are a teen or preteen and hormones cause it

Puberty occurs at different times for different genders and changes different things

Explanation:

For boys puberty traditionally starts at the age of 13 or 14 and lasts a few years. (Not sure how many). But during male puberty your voice starts getting deeper and your erections are more frequent and your private grows longer. After puberty you are able to sperm. This fertilizes eggs in a female body.

For females it can start from anywhere between 8-13. During this time they go on their period. This means that blood from the eggs inside come out of the vagina and causes pain. (That is not quite right but it's the best I have right now). Also while on their period they get cramps that cause almost as much pain as giving birth. After their period they have grown eggs in their body ready to be fertilized.

(I am not 100% correct but I'm sure I wont be the only one answering)