一起means at the same time. The whole sentence means we spend Chinese spring festival and winter holiday at the same time.

in this setence,一起 mean the Chinese new year is one day of winter vacation

A little addition, "寒假" is a holiday of school, which is about one month, usually from January to February. "春节" is a transitional festival, which is the new year in lunar calendar, usually one day in January or February, but also have several days' holiday. So here "一起" means they will have the Spring Festival in their holiday. Kind Regards, Jing W

Actually this sentence has some mistakes. But it means that 春节 (this period) is in 寒假.And 寒假 include 春节(period).

在一起 = together The winter holiday includes the Spring Festival holiday period. 寒假包含春节假期。