What is lines of symmerty?

Answer 1

Lines of symmetry, I think is what you meant to write, is... well it's easier this way:

Think of any shape: in this example we'll use a square. ONE of its lines of symmetry is right down the middle, because then both sides are the same. So, a line of symmetry is a line that divides a shape into to exactly the same shapes (except they are facing the other way.)