High-redshift (z >= 6) star-forming galaxies are a natural tool to study the early galaxy evolution and explore the history of cosmic reionization. In this talk, I will present our recent work on our understanding of these high-redshift galaxies. In particular, I will introduce our on-going program that uses Magellan M2FS to spectroscopically identify a large number of galaxies at 5.5 < z < 6.7 over nearly four square-degrees on the sky. M2FS is a fiber-fed, multi-object (256 fibers) spectrograph on the Magellan Clay telescope. With a large field of view (0.5 degrees in diameter), it is efficient to identify line-emitting galaxies at high redshift. We have observed about three square degrees in a few well-studied deep fields and obtained more than 250 luminous Lyman-alpha emitting galaxies at z = 5.7 and 6.6. This is the largest sample of its kind so far. We are using this unique sample to study a variety of galaxy properties and their implications to cosmic reionization. I will list a few examples of current results, including Lyman-alpha luminosity function, Lyman-alpha emission halos, protoclusters of galaxies, etc.