If your engine has a timing belt, it is absolutely critical that it is replaced at the required interval (typically between 90-105,000 miles). Additionally, you need to ensure that the related tensioner/s and idler pulleys are replaced, along with the water pump (if driven by the cogs on the timing belt).
On many occasions, if this vital rubber timing belt is not replaced, you could sustain damage to the valve train and in some cases will require the replacement of the engine.
We will detail a more technically oriented video in the future, and really just wanted to cover some of the very basic details.