Okay, imagine you have a big book with lots of pages. Each page has a different picture on it. Now, imagine you have a special piece of paper that can stick to any page in the book. This special paper also has some special markings on it that change the picture on the page it's stuck to.
A Clifford module bundle is a lot like this special piece of paper. Instead of sticking to pages in a book, it sticks to points (or positions) in a space called a manifold. Each point in the manifold has a different "picture" called a vector space. The special markings on the Clifford module bundle change this vector space at each point in a particular way.
So, just like you can move the special piece of paper around in the book to change the pictures, you can move the Clifford module bundle around in the manifold to change the vector spaces it's attached to. The way the markings on the Clifford module bundle change the vector spaces at different points in the manifold can tell you a lot about the geometry and structure of the manifold.