M31 is one of the best studied galaxies. At a distance of 700 kpc, it provides us with an opportunity to study the global properties of a galaxy which is similar to our Milky Way. We present our Chandra ACIS observations in the central region and along the disk of M31. We include the following. 1) X-ray spectra of point sources: the energy spectrum provides a hint to the properties of a source; we present the spectra of different types of X-ray sources including supernova remnants, black hole transients in the high state, supersoft sources (SSSs) and sources undergoing state transitions. 2) Statistical overview of SSSs: M31 provides the best place to study SSSs, as the extinction is relatively low and the distance is well known. In our observations, we discovered almost 50 SSS candidates; most of them are newly discovered. We compare the luminosities, colors and environmental dependence of SSSs in different regions. 3) Luminosity functions (LFs) of point sources: we compare LFs of point sources from the bulge and disk regions. It is intriguing that the LFs are different, suggesting different source populations.