What is the difference between a constellation and a star?

Answer 1

A constellation is a "man made" picture of something, depicted by the pattern of a number of stars.

A star is a massive ball of hydrogen and helium, that is undergoing nuclear fusion.

Answer 2

A constellation is a group of stars that form a recognizable pattern in the sky, while a star is a celestial object that generates its own light and heat through nuclear fusion. Stars are individual bodies that can be part of a constellation or exist on their own.