For the moment, what I have is this:
Given the smooth orientedLorentzian manifold, we have the tangent bundle .
We also have the -orthonormal frame bundle, . Now, as we know, is the bundle associated to via
(see associated bundle).
Since has the double cover , we suppose the existence of a "kind of double cover bundle" of , i.e., another principal bundle, with a double cover map (with some additional requirements. I think this is what is called spin structure (see also spin structure in Wikipedia). We then take a vector space over which there is a representation of , this is where the Clifford algebra comes in. The spinor bundle is finally . So the spinor bundle is a vector bundle associated to the double cover of the orthonormal frame bundle.