how to enter a sale without going through accounts receivable?

[red at pixelearth.net]

I have just started with Gnucash, and am happy so far. I have set up my
business account, but I don't understand how to handle the following
basic situation:

How do I enter a payment as a sale without first creating an accounts
receivable transaction? What is the proper "transfer" account when
entering in raw sales money that was not invoiced?

Thanks