Danny, et al., I'm hoping you'll be willing to respond continue this dialog...

What's the different between the private key and the signature?

What does the digital signature consist of? Where did it come from?

Danny says the "private key allows you to provide a digital signature that meets the requirements of specific transaction outputs in order to be allowed to use them as transaction inputs."

Provide a digital signature... to the blockchain, right?

Transactions technically consist of input orders, and output orders?

Why did you say "specific" in "specific transaction outputs"? Do some transaction outputs not require digital signatures?

An example of a complete transaction is one successfully-executed output order plus the successfully-executed input order that the output order triggers?

Neither order will be executed unless a full set of requirements are met? Orders for transactions, such as an output and input order, are carried out only per certain requirements?

One requirement is typically valid order data (such as the currency, the amount...)?
Another is a valid private key?
Another is the digital signature associated with the private key?
Another is confirmation that the private key and digital signature match each other?

Output requirement is
Output requirements are
Output requirements include (a) a valid digital signature and?? the signature must be (b) validly coupled with its private key?

If output requirements are met, the requirements can then be used to try to clear a transaction input?