Hi thanks for your message. It's easy if you've used Radiant or Hammer before.
I will make a video!
in the meantime:
Getting started & Basic Navigation · ViciousSquid/Fio Wiki
Basic concept: Brushes · ViciousSquid/Fio Wiki
* Drag out a box in all three of the 2D views
* Use the "room tool" (first toolbar button) to make it hollow
* Right click in the 2D view and select "player start"
* Click "Play"
The Tools menu can create entire maps (and terrain) quickly
Look at the example maps included.