Question

How do giant stars differ from sequence stars ?

Answer 1

When a star is born it is a main sequence  when the temperature of the star's core becomes high enough to fuse hydrogen into helium. The giant stars are the adult ones, it has a larger radius and luminosity than a main-sequence star. The giant star is the aging process of the star. 

Answer 2

A star is born as a main sequence star when the temperature of the star's core becomes high enough to fuse hydrogen into helium. ... The story is different in evolved stars like giant stars. Once hydrogen in the core of the star is exhausted, the energy generation becomes small and the core starts to collapse. Hope this helps.