when were they there?能这样吗： when were they at there? 会有什么不同？

what did you boss say to him? did是什么用处？怎么用did不用were？

what time do you usually get up on sundays?可以把what time改为when吗？

Were you at the butcher's? 怎么不是：Did you at the butcher's?

What must he do?怎么不是：what must he does?

你的英语单词的词性和用法基本没有掌握，还有句型的构成，以及什么词性或短语作什么句子成分都不是很清楚。该好好听讲了。呵呵

when were they there?不能说成： when were they at there?
there本身是副词，英文解释是in ,at or to that place.在那里的，往那里的意思。可以单独放在系动词be 后作表语。
what did you boss say to him? did是do 的过去式，当句子的时态是过去时的时候，一般疑问句和特殊疑问句的助动词用过去式did，再把谓语动词变成原形。当句子是主系表结构是，用were，比如when were they there?
what time可以改为when，但what time比when 表示的时间具体，what time具体到分秒。
Were you at the butcher's? at the butcher's 是介词短语，用在be 后作表语，不能用Did
What must he do? must是情态动词，后面要接动词原形的。