Initial conditions in a continuum specify the initial field data for the simulation. Examples of initial conditions are:
Each model requires sufficient information so that the model's primary variables can be set. In most cases this is done directly but for some models, such as turbulence models, you may be offered the option of specifying the information in a more convenient form (for example, turbulence intensity and turbulent viscosity ratio instead of turbulent kinetic energy and turbulent dissipation rate).
In steady-state simulations, the solution ought to converge independently of the initial field. However, the initial field still affects the path to convergence, and with it the cost in computing power. Therefore you should specify initial conditions and values judiciously, particularly when the physics is complex.