To Be or Not To Be

Everyone is confused by which "to be" to use, so here I go with the differences of ARU/DA/IRU.

①There is/are; to be (located); to exist (in conjuction with sonzai suru [存在する])
○Teburu no ue ni pen ga arimasu./テーブルの上にペンがあります。
→There is a pen on the table.
○Migi ni magaru to ginkou ga arimasu./右に曲がると銀行があります。
→When you turn right, there is a bank.
○Kono Hoteru ni wa heya ga rokujyuu shitsu arimasu./このホテルには部屋が六十室あります。
→There are sixty rooms in this hotel.

② To have/possess (this is where you treat a direct object with a が instead of を)
○Ane wa kuruma ga sandai arimasu./姉は車が三台あります。
→My sister has three cars!

③There is/are, to take place, to happen
○Nanka atta n desu ka?/何かあったんですか。
→Did something happen?
○Yuube kaji ga arimashita./夕べ火事がありました。
→Last night there was a fire.
○Kyou suugaku no shiken mo arimashita./きょう数学の試験もありました。
→Today, there also was a math exam.

Da is the informal, nonpast form of the copula, which follows nouns and nominal adjectives and expresses meaning roughly equivilent to be identical to or be characterized by. When a noun or adjectival noun is used as a predicate, it is followed by a form of a copula. The Japanese copula thus has a function analogous to some uses of the English verb to be.

○Boku mo gakusei da yo!/僕も学生だよ。
→I'm a student, too!
○Seitotachi wa totemo shizuka da ne?/生徒達はとても静かだね
→The students are very quiet, aren't they?
○Kono hon wa takai desu./この本は高いです。
→This book is expensive.
○ Shiken wa hijyou ni nimusukashikatta desu./試験は非常に難しかったです。
→This test was extremely difficult.

①There is/are, to be (located), to exist The subject when using iru ordinarily must be animate, a person, an animal, an insect, etc.
○Genkan ni dareka imasu./玄関に誰かいます。
→There is someone in the doorway.
○Ashita wa ie ni imasen./明日は家にいません。
→I will not be home, tomorrow.
○Watashi wa shibaraku oba no tokoro ni imasu./私はしばらく伯母のところにいます。
→I will be at my aunt's place for awhile.

②To have (a person that someone has in this sense is treated as a grammatical subject and is marked with　が rather than with を)
○Watashi ni wa kyoudai ga futari imasu./私には兄弟が二人います。
→I have two siblings.

③To be (doing) [in combination with the -te form of a verb, this makes it present progressive] ○Hideo-san to Akemi-san wa hanashiatte imasu./秀男さんと明美さんは話し合っています。
→Hideo and Akemi are talking with one another.

④To have (done) [Again this is used in combination with the -te form, however this is no requirement here the subject be animate)
○Erebeta ga kowarete iru yo/エレベーターが壊れているよ。
→The elevator is broken.
○Hikouki wa mada ugoite imasen/機構木はまだ動いていません。
→The plane hasn't yet moved.

Please do not confuse the verb いる　(居る) with the verb いる　(要る). 要る means "to need" so when you say, "I need money" it would still be "o-kane ga iru." only it uses the kanji 要。