@Daminark: Given a ring A, one defines a sheaf of rings on Spec A. One has a nice basis for Spec A given by D(f) := Spec A \ V(f), f \in A. Now one can show that it is somewhat sufficient to define a sheaf on a base of the topology and that uniquely extends to a sheaf on the whole space. On the base you now define the sheaf O to work like O( D(f)) := A_f, the localization of A on the set {1, f, f², ...}
Now (Spec A, O) is what geometers call an affine scheme and the central object to study in Algebraic Geometry are ringed spaces (Spaces with a sheaf of rings on the space) that locally look …