According to Clifford Algebra: A Visual Introduction,
- A Clifford Algebra over $\mathbb{R}^3$ may describe the rigid motions in space (namely, conjugation acts as a reflection by a plane).
- A Clifford Algebra over $\mathbb{R}^4$ may describe the projective geometry in space.
- A Clifford Algebra over $\mathbb{R}^5$ may describe the conformal geometry in space.
Where could be found an intuitive explanation for the last two items?
Scroll to the bottom of Clifford Algebra: A Visual Introduction, right under Clifford the Big Red Algebra and you will find two links:
The story continues with Geometric Algebra: Projective Geometry.
The final chapter is Geometric Algebra: Conformal Geometry.
If you like this intuitive graphical presentation of Clifford Algebra you might also be interested in another item by the same author
Double Conformal Mapping: A Finite Mathematics to Model an Infinite World
in monochrome pdf format, and there is a full color version of that paper here:
Double Conformal Mapping: A Finite Mathematics to Model an Infinite World