Salesforce Flow: Apex Integration

I need a Salesforce expert who can help me integrate an Apex code with Salesforce Flow

I have an auto-launched Salesforce Flow defined.
In Apex, I start the flow like this:
Map<String, Object> context = new Map<String, Object>();
context.put('taskId', tt.Id);
context.put('whatId', tt.WhatId);
context.put('whoId', tt.WhoId);
context.put('ownerId', tt.OwnerId);
context.put('task', tt);
Flow.Interview theFlow = Flow.Interview.createInterview('flowName', context);
theFlow.start();
The Apex side works and the flow is started.
How do I retrieve the context in the actual flow?

Example here: There are some changes in the Task and the task info is put into the context.
In the Salesforce Flow, I want to retrieve the record with the WhatId and update it.
To make it more general, it might be necessary to add the object type if the 'What' record.

The delivery is a working Flow and a GoToMeeting call to go through the Flow code (setting Variable, etc.) and show how to debug a flow.