Passive

My father is a businessman. He built this company in 2008.

Now, the company employs three hundred people.

How old is this company? It was built in 2008.

Three hundred people are employed by the company.

A lot of money was invested in the project.

(somebody invested it, but we don't know who)

Is this room cleaned every day?

(does somebody clean it? - it's not important who)

This company was built by my father.

Three hundred people are employed by the company.

active: clean(s) / see(s) etc.

passive: am/is/are + cleaned/seen etc.

Somebody cleans this room every day.

This room is cleaned every day.

active: cleaned / saw etc.

passive: was/were + cleaned/seen etc.

Somebody cleaned this room yesterday.

This room was cleaned yesterday.