Before you study relativistic quantum-field theory, have a brief look in a good non-relativistic quantum-mechanics textbook on the topic of identical particles and then the socalled "second-quantization formulation", which is a misnomer, because there is only one non-relativistic quantum theory, and thus at most one "quantization", but the historical name stuck.
The "second quantization formulation" is nothing else than quantum-field theory for non-relativistic particles. You'll see that it is completely equivalent to the many-body Schrödinger wavefunction formalism but much more convenient, because with it's creation and annihilation operators it automatically keeps track of the symmetrization/anti-symmetrization of the many-body states, describing bosons and fermions, respectively (in the latter case implementing also the Pauli exclusion principle).
More importantly, the quantum-field formulation of many-body quantum mechanics makes it very easy to extent quantum theory to processes, where particles can be destroyed and created, i.e., when the particle number is not conserved. In non-relativistic quantum theory this necessity only occurs when you use the quasi-particle method to describe collective modes of many-body systems like phonons (i.e., the quantized vibrations of crystal lattices and the collision of electrons with those, etc.).
Now, if you try to make sense of relativistic wave mechanics, you'll find out that the Schrödinger one-particle or fixed-number-of-particle formalism doesn't work for various formal reasons, usually treated in modern introductions of realtivistic quantum theory (don't waste your time with old-fashioned books, where they make the attempt to go through relativistic quantum mechanics, where this failing concept of a "first-quantization formulation" of relativistic quantum theory is followed). Nowadays the argument, why relativisitic quantum theory is most easily formulated in terms of quantum field theory from the very beginning is the observation that as soon as relativistic collision energies are involved (i.e., center-mass kinetic energies that are large compared to the typical mass scale of the lightest particles involved, like in the most simple version of QED, where you have electrons, positrons, and photons as field degrees of freedom), new particles can be created (as long as the conservation laws of energy, momentum and conserved charges are obeyed) and others destroyed. That's exactly what quantum-field theory makes easy to describe. As soon as you learn perturbation theory and Feynman diagrams with some exercise this will occur quite natural to you, the Feynman diagrams being quite intuitive in depicting what's going on in what's called "elementary reactions". This has to be taken, however with a large grain of "quantum salt". Strictly speaking Feynman diagrams are a very clever way to write down the equations for transition-probability rates (S-matrix elements) used to calculate scattering cross sections within perturbation theory!
