Most matches were in the Index to Griffith's Valuation of Ireland, but one was in Passenger and Immigration Lists: Boston. Since I already know that the Michael Conboy I'm looking for lived in Massachusetts, this looks like a good potential match.

To find out more about this volume, you can click "More Information". This will take you to a summary page describing the data volume containing this match:

From the bottom of that page, you can click through to find more details about that volume, such as the specific types of information you're likely to find, date ranges, and other data.

This introduction to the data should give you an idea of whether it will be a useful resource to you — you can compare what you're hoping to find out about your ancestor to what's available. For this example, let's assume we've decided to buy the subscription.