Relation between the first Pontryagin class $p_1$ and the first Stiefel Whitney class $w_1$ as a tangential structure of manifold M

Question

In Characteristic Class, let us define tangential structure of manifold M such as tangent bundle TM.

0. Is there a difference between the Stiefel Whitney class $w_1 =0$ and the first Stiefel Whitney class $w_1=\delta \gamma$ is trivialized? Which case implies the manifold M is oriented?

1. Is the first Pontryagin class $p_1$ defined only when the manifold is oriented (the first Stiefel Whitney class $w_1$ is zero)?

2. When the first Pontryagin class $p_1$ can be trivialized as the $p_1$ structure, is the first Stiefel Whitney class $w_1$ also trivialized thus the manifold is oriented?

If possible, the pedagogical answer will be nice.