You have a few different routes to take. The prerequisite is you will need to have a Opportunity # saved first to relate to an Estimate. Thus going from Estimate to Opportunity we'll need to do a little bit of reverse engineering:
start by Saving All Sections Action to save the Estimate.
(1) Using an Insert Records Into Table Action you will need to create a new Opportunity:
*note CloseDate, OpportunityStage, Name Values (you may want to have that different I chose default settings)
(2) Now that you have the new Opportunity we need to Retrieve it's RecordID and assign it to the Estimate (creating the relationship)
- In a Loop Through Table using a Retrieve Value From Table Action you will need to retrieve the last (Max) RecordID:
(3) Lastly you will need to use an Update Field in Table action to input that RecordID to the Estimate record.
Here's an overview of my full Action Set:
This will create the Opportunity and relate it to the Estimate. From here you can choose the workflow (e.g. open EditOpportunity screen in a Pop-Up).