Stellar physics is a vital part of modern astronomy since stars play an important role in shaping the Universe. To better understand stars, we must understand not only the stellar surface, but also the stellar interior. We can use the waves propagating under the stellar surface to probe stellar inner regions. These waves behave differently, depending on the local environment they travel through (e.g. density, sound speed, rotation). Asteroseismology, the science that investigates the stellar waves, has been an effective tool to research stellar interiors, similar to seismology that allows geologists to study the Earth by earthquakes. We conducted an observational study on the γ Dor stars. These stars pulsate mainly in g modes and r modes, showing period spacing patterns in the power spectra. The period spacing patterns are sensitive to the chemical composition gradients and the near-core rotation, hence they are valuable for understanding the stellar interior. We identified period spacing patterns in about 600 γ Dor stars from the 4-yr Kepler data. Using the Traditional Approximation of Rotation (TAR), we can measure the asymptotic spacings, the near-core rotation rates, and the radial orders. Our results show that the stars rotate more slowly than predicted by theory, and the rotation distribution shows an excess at the slow-rotation side for unclear reasons. Comparing the near-core rotation with the surface modulation signals, we detected the core-to-surface rotation profiles in about 10% stars. The interiors rotate faster than the cores in most stars, but by no more than 5%. We are extending our research to binaries, which give evidence on how tidal effect acts on the spin of stars.