Turbulent flow in the convective envelope generates resonant sound waves trapped in the stellar interiors and observed as non-radial oscillations of the Sun and Sun-like stars. Investigating the observed mode frequencies of the oscillations allows us to improve our knowledge on the internal structure and dynamics of the Sun and Sun-like stars. In this contribution comprising two parts, I summarize basics of helioseismology and discuss effects of stellar magnetic activity on the global seismic parameters. We report statistical behaviors of the global seismic parameters and their implications found in recent analysis we carried out recently. We briefly conclude by discussing issues not to be mentioned here.