How to find out what has been paid to one or more vendors for a specific time frame
One way is to go into Ledgers and Payables → Reports → Vendors → Vendor Audit
Customize your date range according to the time frame you would like to report. The options for This Month, Last Month, etc., refer to the earliest open accounting period.
The resulting report will give all transactions within the date range specified sorted by Vendor then Invoice date.
Note: When previewing the report some fields in the report are hyperlinks which will take you to the actual transaction.
You can also see information about a single vendor using Bills → Find Bill → (select the pertinent vendor) → Search