Timers are used internally by Roblox to time various things within the Wait() Function of the Lua Script (And various other coding).
How it Works
A Timer is an internal function that monitors the movement or rotation of a brick, while ticking a certain amount of time. When the specified time has been reached, the Lua Script will then jump past the Wait() function, and onto another part of the Script. For example, a script may have a wheel moving forward for four seconds, then turn left. Using the Wait() function, the script is able to monitor the time the wheel is moving. Once the script reaches the four second requirement of the function, it will bypass the Wait() function as it becomes true (The four seconds have been reached.