The word perch has two main meanings:

1. A branch, rod, or high place where a bird sits and rests. When you see a robin perched on a fence post or a hawk perched on a telephone wire, they're using these spots as lookout points and resting places. Birds naturally seek out perches that give them a good view of their surroundings. In a birdcage, you'll find wooden dowels or rods called perches where pet birds can sit comfortably. People also use the word as a verb when they sit somewhere high up: you might perch on a stool at the kitchen counter or perch on the arm of a couch.
2. A type of freshwater fish with spiny fins, commonly found in lakes and rivers. Yellow perch are popular with people who enjoy fishing because they're plentiful and taste good when cooked. If your family goes fishing at a local lake, perch might be one of the species you catch.

The bird meaning is much more common in everyday conversation. When someone says they're perched somewhere, they mean they're sitting in a somewhat temporary or elevated position, like a bird that might fly away at any moment.