How is perimeter used in real world?

Several uses come to mind. For one, the perimeter of a building, multiplied by the wall height gives an estimate of how much paint, siding, sheathing plywood, etc. are needed to do some work.

For things with a circular shape, say a small lake, you can tell the distance across the lake by walking the perimeter and dividing that distance by pi to get the diameter, i.e., distance . Doing the same kind of thing on a flag pole allows you to decide how long the screws must be to mount a flag pulley.

Another is using the perimeter of something like a lawn or garden to estimate how much seed, fertilizer, or other material is needed when you know that it should be used as so much per acre/square yard/square foot or other area.