NASCAR vs F1: What are the similarities and differences?

Formula 1 is the highest level of open-wheel racing in the world while NASCAR is the highest level of stock car racing in America.

What do you mean by an Open Wheel Race Car ? What's the difference between an Open Wheel Car and NASCAR (Stock Car)?

An open wheel race car (also called Formula Cars /Single Seaters) is referred to a car whose wheels are outside the cars main body line and they are purpose built road racing cars.

NASCAR referred to Stock Cars are race cars which are built using production cars manufactured by various car companies . A production car is stripped, strengthened with a roll cage (safety cage) with performance upgrades such a stiffer suspension, powerful motor etc. The stock car racing cars resemble sedans which are used in day to day life.