Welcome new Bitcoin user 
I recommend reading/watching a bit about how Bitcoin works. https://bitcoin.org/ is a good start for this.
To answer your question very shortly: Bitcoins are mined. That's how they are created, think of it as dollars being minted. From there, they can be transfered to other wallets.
So when you buy Bitcoins, they move from the seller's wallet to your wallet. That's it.
I recommend reading/watching a bit about how Bitcoin works. https://bitcoin.org/ is a good start for this.
To answer your question very shortly: Bitcoins are mined. That's how they are created, think of it as dollars being minted. From there, they can be transfered to other wallets.
So when you buy Bitcoins, they move from the seller's wallet to your wallet. That's it.
blockchain is not an exchange, you can't buy from it
blockchain.info is just a block explorer, they don't sell anything
Please don't FUD on topics you don't know. From https://blockchain.info/wallet/#/ :blockchain.info is just a block explorer, they don't sell anything