Lattice QCD is a numerical method to simulate QCD observables using advanced algorithms, fast computers. Lattice QCD is able to reproduce the observables of QCD only if in the idealized scenario of infinite lattice size, zero lattice spacing, physical quark mass, and continuous particle momentum. Practically in order to get QCD observables, lattice data need to be extrapolated to the physical value of each of the above quantities. I will give an introduction on Lattice QCD and try to understand how to connect future lattice data to infinite volume. As examples I will show some interesting results which we are recently investigating, pion charge vertex renormalization in finite volume and pion polarizabilities in lattice QCD.