In the Simpliest Terms…….
CASH BASIS REVENUE means you declare it when you RECEIVE the money.
ACCRUAL BASIS REVENUE means you declare it when you EARN the money (usually that is when the invoice is generated whether you receive a portion of the money or none at all at the time the invoice is generated).
CASH BASIS EXPENSE means you expense it when you PAY it.
ACCRUAL BASIS EXPENSE means you expense it when you OWE it, regardless of when you pay for it.