because NR provides extra energy to cells?

It's slightly outside my knowledge are, so I'll try my best, but it may have some errors. Oversimplifying_

If you join two molecules of nicotinamide riboside with a phosphate you can make one molecule of NAD+.

When your cells burn sugar, they actually transform NAD+ into NADH, and later the NADH is "burned" with the oxygen to produce back NAD+ and make a few ATP molecules.

The ATP stores the energy for a short time, until that energy can be used for something useful, like moving your legs or making proteins.

The easy version in school is

  sugar + oxygen -> CO2 + energy

but there are like 50 intermediate steps to capture as much of that energy in a useful form. One of the intermediate steps uses NAD+, that is formed by two copies of nicotinamide riboside and a phosphate.

Thanks!