NAD+ is known as a hydrogen acceptor- that '+' helps it acquire electrons ...
Most of the energy obtained during cellular respiration is obtained by the removal of hydrogen ions and electrons from the substrate, typically glucose. NAD+ is an important intermediate step in this process. The electrons are passed to the electron transport system, which is basically a way of converting potential energy into ATP.
To fully understand, lets jump to photosynthesis for a moment. In photosynthesis, water is split using the sun's energy into H and OH. In doing this, the plant acquires a supply of H, and stores it as C6 H 12O6 or in similar molecules. (Can you see where this is going?)
In respiration, those H atoms and their electrons are 'pulled off' the glucose and reunited with oxygen (via NAD+ and the electron transport system) to make water - and that process releases lots of energy - energy initially trapped by the plant in photosynthesis