By min 3:30 you should have 3 Reapers in your opponent's base wrecking their economy while building more Reapers. You have to be fast, the longer a rush takes in Starcraft 2 the more it becomes just a weak attack. Keep following the build order with a Refinery, a Tech Lab and 2 more Barracks. By this point you should have identified your adversary's base and you should planning for their weak points, meaning the sides where they have no vision. Have 11 SCV and then build your first Barracks at 150 minerals. With the eight SCV you build your first Supply Depot, after you finish this send your SCV to explore the opponent's base.
The objetive of this strategy is to win early, in a single hit damaging your opponent's economy so badly that he just surrenders.
Mastering this technique will get you to Gold easily. Terran Reaper Rush with is one of the most effective strategies for new Terran players, this is particularly useful when the opponent is Protoss, altought you can also use it against Terran or Zerg if you're faster than your adversary at microing and basic macro.