You can read the GeoGebra license here:
Here is the part I believe addresses your question:
GeoGebra and our web services are made available free of charge for
non-commercial users. Most of our users are students and teachers and
they usually fall under our non-commercial license, allowing them to
use and distribute GeoGebra and related materials free of charge at
home and in school.
Other possibly relevant software worth mentioning:
- Blender - if you want to make 3D diagrams or illustrations
- Inkscape - if you want to make 2D vector diagrams or illustrations
Those two applications are primarily for art/design though. If you want to create rather complex mathematical figures, I'm guessing GeoGebra would suit your needs best. I have used all three, each for different purposes.
Edit: If you are concerned with GeoGebra's license, why not ask them?
If you are not sure whether your use is commercial or not, please just
get in touch with us at email@example.com.
If the GeoGebra license will not allow you to use the software free of charge, you most certainly can use Blender or Inkscape for free.