Hey I have about 400 dollars and I'm 15 I want to buy a visa gift card without a parent can I buy it?

You can absolutely buy it, if you have $400 in cash. Just go to a store.

However, be aware that having a Visa gift card does not mean you can buy anything you want, anywhere. If it is not the kind of card designed for online use, you can only use it in a physical store. And if it's for online, if you cannot prove your age, you will be disqualified from age-related purchases, including ordinary PayPal.

Maybe. But even if you do, you might not be able to use it. You almost definitely won't be able to use it online, because cards need to be "activated" before they are used online, and you usually need to be 18 before you can activate it. You might be able to use it in person, in a brick and mortar store, where the card goes in their card-reader machine. But if you don't want to buy anything there, then you'll be wasting your $400.

Yes.