The restaurant was established in 1980 is still very popular today.

was established in 是动词 establish 的被动语态过去式形式。establish 意思是"建立、设立"，被动语态表示"被建立"。 in 1980 表示"在1980年"，这里 in 表示时间点。 was established in 合起来表示"成立于..."，指某个机构或场所被创建的年份。