porting.... is the process of changing the shape / size etc.of the ports feeding air/fuel mix into, and exhaust gasses out of, the cylinder/s.
different shapes sizes and positions (up and down) mated with different engine modifications produce your specific power statistics. porting is an art/skill which is attempted by many and mastered by few. (i am NOT one of them, i have never even tried it, i may sound like i know what i am talking about but i am realy just a dumb aussie)
on top of what The New Guy said reeds are a valve which allows air/fuel mix to enter the crankcase while it is in vacuum (pistons on their way up) and blocks the mix from blowing back into the carbs while in compression(pistons on their way down).