Challenge 1: A Basic Registered-Source Merge — Solution Walkthrough

Steps:
  1. Build a small Calc spreadsheet: columns Name, Amount, 3 rows of
     sample data. Save it.
  2. Register it: Tools > Options > LibreOffice Base > Databases > New,
     browse to the spreadsheet, give it a name (e.g. "SampleRecipients").
  3. In Writer, Tools > Mail Merge Wizard.
  4. Step 1: select the current document as the starting document.
  5. Step 2: choose "Letter."
  6. Step 3 (Insert Address Block): click "Select Address List," choose
     the registered "SampleRecipients" source — this is the wizard
     step that connects to the registered source specifically.
  7. Step 4: create/skip a salutation as appropriate.
  8. Step 5: adjust layout if needed.
  9. Step 7 (Personalize Documents / Preview): this step shows one
     actual row's real data filled into the letter, letting you page
     through different rows before finishing.
  10. Step 8: complete the merge (print, save, or email).

WHY THIS WORKS AS AN ANSWER
------------------------------
Step 3 (Insert Address Block) is where the registered data source is
actually selected and connected — this is the wizard's equivalent of
Word's own "Select Recipients > Use an Existing List," just reached
through a named, pre-registered source rather than a fresh file
browse. Step 7's preview is functionally identical to Word's own
Preview Results: a chance to confirm the layout and real data look
correct before committing to the full merge output.