How do I buy something off the internet without my parents?

I would advise that you don't do that.
Respect your parents.

I simply wouldn't. They'd probably get mad if they found out. Save yourself the trouble and just ask them; if anything you can ask them to get it for you but wait until your birthday or something to give it to you.

Why won't they let you get it?

If it's something they legitimately don't think you should have, then you should respect that.

If they're being mean, then just figure out another way to get whatever it you want so badly.

Even if it were in secret, your parents are bound to find out somehow. They always do. They will know you're hiding something. Most online stores, want the costomers to have credit, and if you are under 18 or 16, they will want your parents or gardians permission. And if your parents won't let you get it, may not sound fair but it could be for a good reason. I don't know what else to tell you.

Sorry but you should really obey your parents on it. What I normally do if I want something online though is offer to buy it myself. I got fifty shades of grey, darker, and freed that way. I just paid my parents how much I was going to pay on their card. I had permission every time I do this. Maybe if you bought it yourself they'd change their mind, but that depends on what you're buying

Maybe get a friend to buy it for you and you pay them back?

Honestly, I have no freakin idea :/

Well first off, if it's Beats earbuds you want, and you have your own money; can't you just go to the store and buy them? It's a really popular brand every electronics store sells them.

Secondly, hypothetically speaking, you could steal their credit card and try to enter the information yourself. However your chances of getting caught are about 110% because your parents will either
A. catch you with their card
B. notice the charge on their credit card bill, cancel it, and never let you get anything online ever again
C. Notice you with the headphones and make you return them.

Long story short, look for them in stores and buy them with your own money if you have it, otherwise just wait, maybe you can try getting them as an early Birthday present or something?