The difference between a triangle and a square is that a square has 4 equal sides and has 4 right angles, while a triangle has 3 regular angles (if a right triangle, it will have 1 right angle and 2 regular angles) and sometimes can have equilateral sides (equilateral triangle) and other triangles like an isosceles triangle, a right triangle, an obtuse triangle, an acute triangle, and a scalene triangle.
Hope this helped!
Nate