The official py4vasp Python package can be used to automatically parse most VASP output parameters. Pymatgen also has several utilities for VASP output parsing.
OUTCAR for a simple geometry optimization of MOF-5.
The primary output file in VASP is called the OUTCAR file. There is a ton of info in it. Here are the most important things:
Iteration: This line specifies the iteration of the geometry optimization procedure and the SCF loop for that given geometry. A value of Iteration 4( 2) would indicate "geometry step 4, SCF iteration 2."
energy(sigma->0): The value following this line is the current iteration's energy. The unit is eV.
magnetization (x): If LORBIT is set to >= 11, the atom-wise spin moments are printed in this table, each in units of Bohr-magnetons.
A more structured output can be found in vasprun.xml and vaspout.h5 (if VASP is configured to support it).
CONTCAR
The CONTCAR file is formatted identically as the POSCAR file but contains the most recent set of atomic positions and cell parameters. When restarting a calculation, you can copy the mv CONTCAR POSCAR to continue the geometry optimization process.
Volumetric Files
CHGCAR: If LCHARG = .TRUE., the charge density will be written out in this file.
WAVECAR: If LWAVE = .TRUE., the wavefunction will be written out in this file. This is particularly useful when restarting calculations, as they will automatically read this file.
Other Files
DOSCAR: Data about the density of states.
EIGENVAL: Data about the Kohn-Sham eigenvalues.
OSZICAR: Contains data for each SCF iteration. Useful for identifying SCF convergence issues.