I am new and I am catching onto the knowledge slowly.
I have a:
coinbase account with public key(I can't find a private key)
blockchain account with public key(I can't find a private key)
paper wallet with public and private key.
1st I thought you needed a private key to send money....why doesn't coinbase or blockchain have a private key?
Coinbase works like a bank.
When you deposit 10000 USD in your bank account, you no longer directly control that 10000 USD. Instead you get a 10000 balance on your bank account.
Similarly, you can't control your bitcoin directly on your coinbase account, and so only coinbase (not you) has the private key.
For blockchain.info, you should be able to find your private keys in the "Import / Export" tab.