I am starting to learn QFT and I am scanning my text (Mandl and Shaw) for the highlights. Would some please confirm whether these are the highlights. (1) The states are Fock states where the states are distinguished by occupation numbers for various single particle or single photon states. (2) These states are operated upon by operator-valued fields to annihilate or create particles or photons in single particle or single photon states at field points. (3) The Lagrangian of the operator valued fields governs the space-time dynamics of the operator-valued fields and thus the dynamics of particle or photon creation and annihilation.