What are ways to divide square into 4 equal parts?

There is an infinite number of ways; easy ones are:

1- Cut it along the diagonals. (you get 4 triangles)

2- Cut vertically and horizontally through the center. (you get 4 squares)

More generally (this is a bit tricky): Imagine a cross with its center at the center of the square, now rotate the cross as much as you want (as if you were playing the game twister). If you cut it along the imaginary cross, the four parts will be equal.