I am very new to differential geometry. I am familiar with fibered manifolds, fibered bundles (i.e fibered manifold with local trivialization) and sections. No I want to motivate the existence of local sections and for that I am looking for an example of a fibered bundle that admits no global section. Can someone tell me in which book I can find such an example. It would be best if it is very basic. I now there is the example of the slit tangent bundle of $S^2$ but I haven't introduced tangent bundles and I haven't found a good one anywhere else.