In Japanese, the verb aru is used to signify the existence of something, while the verb iru is used to signify the existence of someone. They shouldn’t be used interchangeably, even though they both mean, "to be", or "exist".
You would do well to get acquainted with these two Japanese verbs because they are used so frequently. Aru is for inanimate subjects or objects, while iru, is for animate subjects or objects. Iru is used when speaking of the existence of living things but more particularly, people; Aru is used when speaking of the existence of things (inanimate objects, books, pens, lakes, trees.) Aru has other honorific forms. Its' most common polite form is arimasu. Iru can take other honorific or polite forms too, like imasu, irrashaimasu, or orimasu.
If it breathes use iru if not, use aru. Here is a summary and examples:
IRU (v. to be) - People, Animals.
ARU (v. to be) - Place, Things.
1. There is a book on the table. - テーブル の上に本があります Teburu no ue ni hon ga arimasu.
2. There is a red car placed there. - 赤い車がすそこにおいてありますAkai kuruma ga soko ni oite arimasu.
3. How many marbles do you have? - B 玉はいくつありますか? B-dama wa ikutsu arimasu ka?
When dealing with live, breathing creatures (i.e animals, humans, and usually even some insects like the kabutomushi兜虫, use iru.
1. Is Mr. Tanaka Home? -
Tanakasan irrashaimasu ka? 田中さんいっらしゃいますか?
Tanakasan imasu ka?
To which one could reply, “Hai, orimasu.” はいおります “Yes, he is home.”
2. I have 6 cats. – 猫ろっぴきがいます Neko ga roppiki imasu.
3. How many brothers do you have? - 兄第は何人いますか Kyo^dai wa nannin imasu ka?
4. How many are there? なんこある nanko aru?