If you find a scanned copy, support the author by printing the first chapter from a legal preview. If you love it, buy the physical copy from the AMS. But whichever route you take, read it. Your ability to visualize geometry will never be the same.
provides a clear overview of how Macdonald transitions from standard linear algebra to geometric algebra. Casual Introduction : If you prefer a less formal summary, the article A casual intro to Geometric Algebra