The four areas
How a workflow runs
You drag tools onto the canvas and connect them with anchors — the small shapes on each side of a tool. Data flows left to right along those connections.
Each tool takes rows in, does one thing, and passes rows out. That constraint is what makes workflows readable: you can point at any connection and say exactly what the data looks like there.
Running and inspecting
Run the workflow with the Run button or Ctrl+R. Then click any connection to see the data at that point in the Results window, along with the record count.
Check the record count after every tool that could change it — Join, Filter, Union, Summarize. A workflow that produces wrong numbers almost always does so because a record count changed somewhere unnoticed.
Messages
The Results window has tabs for messages, warnings and errors. Warnings are worth reading rather than dismissing — field truncated, conversion error, and record limit reached all mean data changed silently.