Your bicycle's drivetrain is comprised of all of the parts that power the bicycle and make it go. Bike pedals move the cranks, which turn the bottom bracket and the chainrings, which drive the chain that spins the rear sprockets, turning the rear hub, which moves the wheel and propels the bicycle forward. The crisp movement of these parts and the ability to minimize effort while maximizing speed is the heart of cycling. It is essential that your drivetrain be clean, true and well-maintained in order to more fully enjoy riding your bike. When one of these parts gets out of whack, the rest soon follow.
It is also important to get individual components that are compatible within the system (e.g. typically Campagnolo and Shimano parts are not inter-compatible). Many times the difference between 9- and 10-speed parts is enough to make them incompatible as well. The collective term for a complete bike drivetrain kit is "group" or "gruppo." Multi-speed drivetrains are classified by the number of cogs in the rear cassette. A modern day 10-speed bicycle can have as many as 30 "possible gears," with 10 in the rear and three in the front, but still have a 10-speed drivetrain.
Your pedals are the power transfer points between you and your bike. As you pump your legs and turn your feet, you cause the cranks to turn. Proper pedal choice is important for comfort, control and safety on the bike. Many recreational and enthusiast cyclists prefer the adaptability that platform pedals offer. They allow you to ride in any type of shoe and give a sense of security to a novice rider who is cautious of locking the feet into clipless pedals. Many platform pedals can be adapted with a toe cage to give more control and power while retaining the sense of security associated with platforms.