A square is a geometrical figure that has 4 congruent sides and angles. This means all side lengths and angles are the same.
A rectangle is a geometrical figure that has 4 similar sides but are not the same length. However, a rectangle does have congruent angles. A rectangle has 2 sides that are double the other 2 sides, in which both of each (length & width) have the same measurement.
I hope this helps!