| Meteors fall into the Earth's atmosphere all the time... tons of them every year. But when the Earth passes through the debris left behind by a comet, then you get lots of meteors at once.... a shower.
The most activity is usually just before local dawn that's when you are rotating in the same direction that the Earth is travelling around the Sun.
A couple of examples: the Perseids (around August 12) and the Leonids (around November 17). | 
