Formal:
* Мы закончили. (My zakonchili) - This means "We have finished."
* Вы закончили? (Vy zakonchili?) - This means "Have you finished?"
Informal:
* Мы сделали. (My sdelali) - This means "We did it."
* Ты сделал? (Ty sdelal?) - This means "Did you do it?"
More specific:
* Мы закончили работу. (My zakonchili rabotu) - This means "We finished the work."
* Я закончил читать книгу. (Ya zakonchil chitayt knigu) - This means "I finished reading the book."
The best way to choose the right phrase is to consider the context of the conversation.