Direct Passive vs. Indirect Passive

In English, the passive form is used to tell something that was done on an object. For example,

"The car was repaired by the mechanic."

Note that in English, only transitive verbs (verbs that require objects) can be converted into a passive form. Thus, there are no passive forms for verbs like "go", "sneeze", and "die".

There is an exact equivalent of the English passive form in Japanese, which is called the direct passive form. The passive form is constructed as follows:

1. Godan verbs:
nai-stem + reru

ex. 使う "tsukau" -- 使われる "tsukawareru"

2. Ichidan verbs (aka "iru" or "eru" verbs)
nai-stem + rareru

ex. 食べる "taberu" -- 食べられる "taberareru"

3. Irregular verbs

する "suru" -- される "sareru"
くる "kuru" -- こられる "korareru"

The following sentences can be translated into Japanese directly:

These tools are used in building a house.
これらの道具は家を建てるのに使われる。
Korera no dougu wa ie wo tateru no ni tsukawareru.

It is said by everyone that (I'm/it's) strange.
みんなに変だと言われます。
Minna ni hen da to iwaremasu.

There is also another "form" of the passive in Japanese, called the indirect passive. This can also accommodate intransitive verbs, and has no direct equivalent in English. It is used to denote an action that was done by someone on the subject that is out of the subject's control. Most textbooks on Japanese call this the suffering passive, as this form is mostly used to denote an event that is unfortunate. An interesting insight by Tae Kim is that there is no such thing as a "suffering" passive: what makes the passive indicate "suffering" is that the action is done on the object without the object's control. This may make it easier to understand for some learners of Japanese.

The agent responsible for the inconvenience is followed by に. Compare the following sentences:

あの犬が足をかんだ。
Ano inu ga ashi wo kanda.
That dog bit (my) leg.

あの犬に足をかまれた。
Ano inu ni ashi wo kamareta.
(I) was bitten in the leg by that dog.

In Japanese, the 2nd sentence (which uses the passive form) indicates that the event is something unfortunate or something outside the subject's control (i.e., you couldn't help it but you were bitten in the leg by the dog), whereas the 1st sentence is more neutral.

When an intransitive verb is used in the passive form, that is most definitely a case of the indirect passive.

ex. 夫に死なれた女性は未亡人と呼ばれる。
Otto ni shinareta josei wa miboujin to yobareru.
A woman whose husband has died is called a widow.

In the example above, there are two verbs in the passive form: 呼ばれる and 死なれる. 呼ばれる is used in the direct passive sense (i.e., there is no indication of something unfortunate). The use of the passive form "shinareta" 死なれた indicates that the action of the husband dying affected the woman in some way.  Contrast this with a sentence using the active form instead:

夫が死んだ女性は未亡人と呼ばれる。
Otto ga shinda josei wa miboujin to yobareru.

This is a more neutral construction, and the tone conveys a matter of fact.


Reference:
Ultimate Advanced Japanese, Random House.
Tae Kim's Guide to Japanese blog. http://www.guidetojapanese.org/blog/2005/09/09/no-suffering-passive/
jisho.org (for example sentences)