although spivaks comprehensive text is the best overall diff geom book out there, it is so loong you can get lost or bogged down.
you might try some easier books like Noel J Hicks, or do Carmo, or Ted Shifrin's notes availablef ree from his website at University of georgia first.
Spivak spends an entire thick book, vol 1, on foundations of diff manifolds, a bit of a heavy meal. then vol 2 is a fantastic intro to the curvature tensor, the heart of diff geom. then it just goes on from there.
so if you get bored in vol 1 just go on to vol 2 for the geometry and refer back to vol 2 for needed facts. of course you need the definition of a manifold and a tangent space but that's about all.
a very easy book to read on a closely related subject diff top, is by guillemin and pollack, and intended for undergrads.