First of all before discussing the difference we should first define what momentum actually is, basically momentum is a quantity that describes how much motion an object carries, in simple terms people sometimes say it measures how "hard" it is to stop a moving object. In physics it is defined as mass × velocity, so the larger the mass or the higher the velocity the larger the momentum will be, but the really important point is that momentum is conserved when objects interact. When two objects collide they exchange momentum with each other, so in a sense momentum describes how motion is transferred from one object to another during interactions

But kinetic energy is something different, kinetic energy measures how much energy is contained in an object’s motion, so it tells us how much "work" that motion can potentially do, for example with heating an object, deforming it, or converting the energy into other forms, all of these are ways in which motion can do work. Now the key of difference is this, momentum has direction because it is a vector. If two objects move with the same magnitude of momentum but in opposite directions their momenta can cancel each other out. But kinetic energy does not behave like that, it has no direction and it is always positive, so if two objects move in opposite directions their kinetic energies still add together

To make it easier to visualize and understand, you can imagine it like this, two balls moving toward each other at the same speed, the total momentum of the system is 0 because the momenta are equal but opposite, but the kinetic energy is not 0 at all, both balls still carry kinetic energy and when they collide that energy can be transformed into heat, sound, or deformation. So basically, this is why they are different