Information about convergence speed and about the current step is written to stdout and to the file OSZICAR. Always keep a copy of the OSZICAR file, it might give important information.
Typically you will get something similar to the following lines:
reading files
WARNING: wrap around errors must be expected
entering main loop
N E dE d eps ncg rms rms(c)
CG : 1 -.13238703E+04 -.132E+04 -.934E+02 56 .28E+02
CG : 2 -.13391360E+04 -.152E+02 -.982E+01 82 .54E+01
CG : 3 -.13397892E+04 -.653E+00 -.553E+00 72 .13E+01 .14E+00
CG : 4 -.13400939E+04 -.304E+00 -.287E+00 84 .48E+00 .39E-01
CG : 5 -.13401306E+04 -.366E-01 -.322E-01 69 .35E+00 .17E-01
CG : 6 -.13401489E+04 -.183E-01 -.169E-01 75 .74E-01 .66E-02
CG : 7 -.13401516E+04 -.267E-02 -.250E-02 68 .47E-01 .37E-02
CG : 8 -.13401522E+04 -.567E-03 -.489E-03 53 .15E-01 .90E-03
1 F= -.13401522E+04 E0= -.13397340E+04 d E = -.13402E+04
trial: gam= .00000 g(F)= .153E+01 g(S)= .000E+00 ort = .000E+00
charge predicted from atoms
charge from overlapping atoms
N E dE d eps ncg rms rms(c)
CG : 1 -.13400357E+04 -.134E+04 -.926E+01 56 .97E+01
N is the number of electronic steps, E the current free energy,
dE the change in the free energy from
the last to the current step
and d eps the change in the bandstructure energy.
ncg the number of evaluations of the Hamiltonian acting onto a
wavefunction, rms the norm of the residuum ( 
)
of the trial wavefunctions (i.e. their
approximate error) and rms(c) the difference between input and
output charge density.
The next line gives information about the total
energy after obtaining convergence.
The first values is the total free energy F (at this
point the energy of the reference atom has been subtracted),
E0 is the energy for 
(see section 9.4),
and d E
is the change in the total energy between the current and the last step;
for a static run dE is the entropy multiplied by sigma.
For a molecular dynamics (IBRION=0 see section 7.19) this line will is a little bit different:
1 T= 1873.0 E= -.13382154E+04 F= -.13401522E+04 E0= -.13397340E+04
EK= .19368E+01 SP= .00E+00 SK= .00E+00
T corresponds to the current temperature,
E to the total free energy (including the
kinetic energy of the ions and the energy of the Nosé thermostat).
F and E0 have been explained.
EK is the kinetic energy, SP is the potential energy
of the Nosé thermostat and SK the corresponding kinetic energy.
Additional technical parameters and some status reports are also written to stdout.