We present the results of the lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants, recently performed with N f = 2 dynamical fermions by the ETM Collaboration. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non perturbative RI-MOM renormalization procedure. Our results for the light quark masses are mMS ud (2 GeV) = 3.85± 0.12± 0.40 MeV, m MS s (2 GeV) = 105± 3 ± 9 MeV and ms/mud = 27.3± 0.3± 1.2. We also obtain fK = 161.7± 1.2± 3.1 MeV and the ratio fK/ fπ = 1.227± 0.009±0.024. From this ratio, by using the experimental determination of Γ(K → μν̄μ(γ))/Γ(π → μν̄μ(γ)) and the average value of |Vud | from nuclear beta decays, we obtain |Vus|= 0.2192(5)(45), in agreement with the determination from Kl3 decays and the unitarity constraint.