$1.$ Money is collected by John.

- S + is/ are + V (Pii) + (by O).

$2.$ The window was opened by Hoa last night.

- S + was/ were + V (Pii) +(by O).

$3.$ Our homework was done yesterday.

- S + was/ were + V (Pii) +(by O).

$4.$ English is taught by him in our class this year.

- S + is/ are + V (Pii) + (by O).

$5.$ A lot was eaten by the sheep last night.

- S + was/ were + V (Pii) +(by O).

$6.$ Our rooms aren't cleaned today.

- S + is/ are + not + V (Pii) + (by O).

$7.$ A letter is written to her friend.

$8.$ My purse was stolen 5 days ago.

Ex2: 

1. John collects money.

$\longrightarrow$ Money is collected by John.

2. Hoa opened the window last night.

$\longrightarrow$ The window was opened by Hoa last night.

3.We did our homework yesterday.

$\longrightarrow$ Our homework was done by us yesterday.

4. He teaches English in our class this year.

$\longrightarrow$ English is taught in our class by him this year.

5. The sheep ate a lot last night.

$\longrightarrow$ A lot was eaten by the sheep last night.

6. We do not clean our rooms today.

$\longrightarrow$ Our rooms aren't cleaned by us today.

7. She write a letter to her friend.

$\longrightarrow$ The letter is written to her friend by her.

8. Somebody stole my purse 5 days ago.

$\longrightarrow$ My purse was srolen 5 years ago.

Bonus: 

* Present simple:

S + V(s/es) + O

$\rightarrow$ S + am/is/are + PII

* Past simple:

S + V(ed/Ps) + O

$\rightarrow$ S + was/were + PII