Brian,
To create reports you can download our Report Designer here if you haven't already.
By default, estimates are not linked to opportunities. You could start by adding the opportunity number (RecordID) as a drop down field into the Estimate table. If you then add the field to your estimate screen, you'll be able to choose which opportunity an estimate is linked to. Remember that opportunities don't have to be estimates. They could be anything from a current customer casually asking about a new product, to a lead about to close a deal. Once the opportunity number is added to the Estimate table you can link other fields from the Opportunity table such as the OpportunityStage and the ProbabilityPercent.
In the Report Designer, you can edit the stock Estimate(Custom) or SimpleEstimate reports (remember to edit a copy of the report to keep the stock one intact), or create a brand new report from scratch. For some help with the Report Designer, we have some useful webinars here and here.
Here are the pages again for an in-house consultant and our Method Solution Providers if you need them. Hope this helps!
Jason