"They go out for a picnic" 中文可以说作 "他们出去野餐"。
其中 "go out" 意思是 "出去"，"for" 意思是 "为了"，"a picnic" 意思是 "野餐"。
一些例句:
"They're going out for a picnic this afternoon." (他们今天下午要出去野餐)
"I heard they're planning to go out for a picnic next weekend." (我听说他们计划下个周末出去野餐)
"I think it would be nice to go out for a picnic today." (我认为今天出去野餐会很好)