# Coordinate principal bundle over a curve

I am trying to understand more about geometric interpretation of vertex algebras following "Vertex Algebras and Algebraic Curves" by Ben-Zvi and Frenkel, but I am in trouble with the following constrution:

Let $$X$$ be a smooth curve over a algebraically closed field $$k$$ of characteristic zero, $$p \in X$$ a $$k-$$point and $$\hat{\mathcal{O}_p}$$ be the completation of the local ring, then $$\hat{\mathcal{O}_p} \simeq k[[z]]$$. Let $$G_0(R) = \{f \in \mathrm{Aut}(R[[z]])| f(z) \in z R[[z]] \}$$ be de group-scheme of automorphims of the formal disc preserving the origin and $$\mathrm{Coord}_p = \{\hat{\mathcal{O}_p} \to k[[z]] \,\,\,\text{isomorphism}\}$$, $$\mathrm{Coord}_p$$ is a $$G_0(k)-$$right torsor. I would like to construct a $$G_0-$$principal bundle $$\mathrm{Coord}_X$$ over $$X$$ with fiber $$\mathrm{Coord}_p$$ at $$p$$. Frenkel and Ben-Zvi actually gives a functor of points $$F(R) = \{f: R[[z]] \to X \,\, \text{with non-vanishing differential at}\,\, z=0\}$$.

I am looking for references to:

1. Principal bundles over schemes (with Zariski opens) and associated bundle;
2. A construction of this $$\mathrm{Coord}_X$$ or anything similar to understand better what is going on.