We live in a colourful and a beautiful environment. When we observe the things around us, we can find that these things are made in perfect ratios.
For instance, imagine a train with many compartments. Each compartment from the outside looks identical.
Similarly, observe the petals of a flower. We can find that they are identically made.
This identicalness is called symmetry.
Symmetry is everywhere. It is present in both natural and artificial bodies. Natural bodies might include leaves, butterflies and so on, whereas artificial bodies might consist of human-made constructions.
An object is said to be symmetrical when you cut the thing into two and both the halves look identical. The two symmetrical halves are like a mirror image, and they complete each other.