http://investr4zcyv3issfcryd7mqiflbedhtbt6h4mnbd6b2qshg7sevffad.onion/simple-bitcoin/index22.html
Typically, a single party is exchanging some value of Bitcoin for another asset or service with another Bitcoin wallet. When this occurs, every individual Bitcoin wallet will use its secret data to sign and validate transactions, providing mathematical proof that the buyer or seller is the owner of their Bitcoin wallet.