The passive form of verbs in Japanese is formed by the following:
1. Type 1 Verbs (godan) -- replace the -u with -(w)areru
ex. iu -> iwareru; nomu - nomareru
2. Type 2 Verb (ichidan) -- replace the -ru with -rareru
ex. taberu -- taberareru
3. Special Verbs
ex. suru -- sareru, kuru -- korareru
The resulting passive forms conjugate like Type 2 verbs.
ex. iwareru -- (past) -- iwareta
Unlike the English passive voice, the Japanese passive voice can only be used for person-to-person or animal-to-person actions, if there is no misfortune to be implied.
If person 2 does something to person 1, then the sentence construction is:
(Person 1) wa, (Person 2) ni (Passive form).
ex. I was scolded by my mother. -- Watashi wa, haha ni shikarareta (shikar(areru)).
ex. I was bitten by a mosquito. -- Watashi wa, ka ni sasareta (sas(areru))
ex. Tsukasa asked me to go out with him. -- Tsukasa-kun ni tsukiaou to iwareta.
However, when talking about person-object actions, the passive form is not used.
ex. This bag was bought by me.
Kono kaban wa, watashi ni, kawareta. (X)
Kono kaban wa, watashi ga katta. (/)
ex. That umbrella was left at the taxi.
Sono kasa wa, takushi de wasurerareta. (X)
Sono kasa wa, takushi de wasureta. (/)
The object is used as the subject, and the active form of the verb is used to describe what happened to the object.
When the action is not directly done to a person, but rather to a thing owned by the person, and if that action is detrimental to that person, then one can also use the passive form.
(Person 1) wa, (Person 2) ni (Object owned by Person 1) wo (Passive form).
ex. My hand was bitten by a dog. -- Watashi wa, inu ni, te wo kamareta. (kam(areru)).