Action of right angled Coveter group on its Davis complex

Question

For any right-angled Coxeter group $W_{\Gamma}$, we denote the Davis complex by $\Sigma_{\Gamma}$.

I wonder how to see $W_{\Gamma}$ acts on this complex (by left multiplication) with finite stabilisers? Moreover why thus, any torsion-free subgroup of finite index acts freely on $\Sigma_{\Gamma}$?