As a D-brane and an anti-D-brane (which span the 3 spatial dimensions of our universe) move towards each other, the cosmic scale factor (i.e., the size of the universe) grows exponentially, so the radiation and matter densities are rapidly diluted. This is the inflationary epoch. As is well known, inflation solves the flatness problem, the horizon problem, the defect problem and the angular momentum problem. The density perturbation produced during inflation will eventually be the seed for structure formation, as well as the temperature fluctuation seen in the cosmic microwave background radiation. Inflation ends when the branes collide and annihilate. The energy released from the annihilation heated up the universe, starting the radiation-dominated hot big bang epoch. Cosmic strings were also produced during the brane collision. The properties of the cosmic strings are quite model-dependent. If they are (meta-)stable, they would evolve to a scaling network and provide a clear signature to be detected in the near future, via gravitational lensing, polarization in cosmic microwave background radiation and/or gravitational wave bursts in LIGO II/VIRGO/LISA. If so, cosmic string opens a window to the superstring theory.