I have tried to use the templates 7 for fun, and must admit
that I neither understand how they work or how to aproch to use
them by starting with the explanations in the included manual.

How should a Beginner fizzle that out without beeing totally
frustrated?

You need to do the following:

in the manual, in the introductory page:
link to a "Quick Start for Beginners" Page.
On this, dont explain technical details, but make a
Stap-by-Step list how to load a "Beginner Level" in Wed,
let the Beginner add 2 Enemies, and then hit compile+run.

This way the Beginner is happy to
1: undertand how he starts up the core editing tool (WED)
2: how to make changes to the worls on his own (Enemies)
3: how to compile and enjoy the results

In the following "Steplist" you can introduce how to build
up a simple Shooter-level from scratch, etc.