this trip was the first time （that）i had to use english in real life.
这句话的意思是：这次旅行是我第一次用英语于现实生活中.
这是个定语从句this trip was the first time是主句,the first time是先行词,后面的i had to use english in real life是从句修饰the first time,time后面省略了连词that.