Likewise, in any completely closed mechanical system mass will be conserved. Now conservation of momentum is fairly easy to understand, also. It's basically a statement of what intuitively is inertia. The bowling ball rolls until stopped by the pins and backstop. Similarly, the dishes stay on the table, despite the small amount of force from the tablecloth's being yanked from under them.
Energy conservation is a bit more complicated, because energy comes in so many forms.
Here's an example, however. I drop a vase from a building. Initially, there is a large amount of gravitational energy in the vase, which results from my having carried it to the top of the building. After I drop it, gravitational energy rapidly becomes kinetic energy, and by the end of the fall, all of the gravitational energy I introduced by carrying it up has been converted to kinetic energy. At that point, the vase shatters, and kinetic energy is converted into the energy that breaks the vase and destroys the chemical bonds that held the vase together.