Field notes
The Introduction is the opening section of your PDF export, and nothing else. It does not add a working canvas. It is only the prose that greets the reader before the tabs are laid out.
Leave the editor empty to use the standard text (it adapts to the solution's language). Write your own text in the editor to store a unique introduction for this particular solution, and clear the field again to fall back to the standard text. The label above the editor shows which one is active, "Auto" or "Custom".
The tab is hidden by default. Turn it on under Settings → Show / hide tabs when you want to write your own introduction for your solution.
A good introduction is short and orients the reader about:
Keep it to about a page. The details live in the tabs themselves.