检测Box2d和libgdx（android）中两个物体之间的碰撞

I am new to libgdx and Box2d engine and I'm developing a game using same .I want to detect collision between two bodies to perform some function.But I'm not aware about the optimum way to do that and also want get point of collision.Kindly provide some suggestion with code.I have already implemented ContactListener but to no avail.I am new to libgdx and Box2d engine and I'm dev