Historical Cost Principle: Assets and liabilities should be recorded at the price at which they were acquired. This is to ensure a reliable price; market values can fluctuate and be different between differing opinions, so the price of acquisition is used.
Matching Principle: Expenses should be matched with revenues. The expense is recorded in the time period it is incurred, which means the time period that the expense is used to generate revenue. This means that you can pay for an expense months before it is actually recorded, as the expense is matched to the period the revenue is made.
Revenue Recognition Principle: Revenues should not be recorded until the earnings process is almost complete and there is little uncertainty as to whether or not collection of payment will occur. This means that revenue is recorded when it is earned, which means the job is complete.