To realize an unfigured bass, first determine the harmonic functions projected by the scale-degree progression in the bass. Then choose figures for each bass note consistent with those functions. Lastly, realize the resulting figured bass according to the usual procedures.
The following chart provides the most common functions for each diatonic scale degree and the most common figures for each functional bass type. Keep in mind that once you have determined the functional progression, you may change the specific figures to smooth out the voice leading in the final realization.