Theory vs Computation

For theory they collect data, observe phenomena and try to fit an equation that approximates or predicts the result. the behavior, then they test the equations to verify if it reproduces de experiment, if all fits well then It becomes a field of study. Simulation comes next and its how the field its studied, by the equations without having to experiment.
I believe these two concepts can be easily mistaken since there are fields where theories still need to be tested, the difference would be that one comes after the other.