How rockets are controlled during flight

Most of you have probably seen that some space rockets and most water rockets use fins in the bottom part of them. That's because they are one way to control rockets during fly and, by far, the cheapest, so it's convenient to use them. The other ways are gimbaled thrust, vernier rockets and thrust vanes.

Image by Nasa

• Fins: They are used to change air direction to generate thrust in the direction the rockets need to go. In addition, they are very easy to built and are the most used for water rockets. There are different forms of them to control the drag they produce.
• Gimbaled thrust: It consist in changing the direction of the exhaust by moving the nozzle to change the thrust direction. They are used in most of space rockets and aren't use in water rockets because its complexity.
• Vernier rockets: They are small rocket engines that can be in the bottom or top of space rockets. They are used for short periods of time to add a extra thrust in one direction. 
• Thrust Vanes: They are small vanes located on the bottom of the rocket to change the exhaust direction by there movement. They were used in the past by space rockets but not now.