You are obviously confused Coinbase.com with coinbase in transaction. They are two different things. Coinbase.com is a wallet and exchange. coinbase in transaction is
coinbase transaction, has no inputs. It is created by miners, and there is one coinbase transaction per block. Because each block comes with a reward of newly created Bitcoins (e.g. 50 BTC for the first 210,000 blocks), the first transaction of a block is, with few exceptions, the transaction that grants those coins to their recipient (the miner). In addition to the newly created Bitcoins, the coinbase transaction is also used for assigning the recipient of any transaction fees that were paid within the other transactions being included in the same block. The coinbase transaction can assign the entire reward to a single Bitcoin address, or split it in portions among multiple addresses, just like any other transaction. Coinbase transactions always contain outputs totalling the sum of the block reward plus all transaction fees collected from the other transactions in the same block.
Some of the useful sources:
•
https://bitcoin.org/en/developer-reference#term-coinbase-tx•
https://en.bitcoin.it/wiki/Protocol_documentation#Transaction_Verification•
https://bitcointalk.org/index.php?topic=141616.0
