How from a local system $\mathcal{F}$ with value in an R-module over a topological space $X$, can we associate a representation of $\pi_1(X)$?
More precisely, how does $\pi_1(x)$ act on the stalk $\mathcal{F}_x$ concretely? and why does it induce a representation?
I found the proof in the book of Szamuely "Galois groups and fundamental groups" page 51 Theorem 2.5.15, however it is not evident from me why the addition should be a map of $\pi_1(X)$-sets.