Question : How do I create one report which combines multiple tables?

I am creating two tables: one is for contracts and the other is for contract addendums. The addendums will be related to the contract table through the contract unique identifier. We track the overall project and then all the changes (addendums).

Is there a way to create a report that combines the contracts and addendums  and displays a row for each?

The results would be like this:
Contact 1
Contract 1 addendum
Contract 2
Contract 2 addendum
Contract 2 addendum b

Answer : How do I create one report which combines multiple tables?

Yes, FM does this well.  You will use the addendums as the body data and the contract as sub summary data.  Using the relationships you have the sub summaries print when the contract changes.