difference between desu and iru and aru?

Is desu just the polite version of aru and iru? Can desu be used for both ?

No and no.

"desu" is the polite version of "da," the "be" verb in English.

"iru" and "aru" have their own respective polite forms: "imasu" and "arimasu."

I think that it is a good idea to think of desu as "IT is" and arimasu/imasu as "THERE is," or perhaps just "exists." Try to imagine what might come before desu or arimasu/imasu to get a better idea of the differences.

A: ano biru wa nan desu ka?
B: eki desu.

A: asoko ni nani ga arimasu ka?
B: eki ga arimasu.

Of course it's far more complicated than the examples suggest but I think this is a good way of looking at it as a beginner.

Ive heard that desu is used to say 'is' and aru,iru is used to express something about an object or someone

please try the Kanji conversion, at facing trouble.
Maybe it's the best way.
1. desu: です　　 （Modal verb)
　Polite language of "is".
2. aru : 有る/在る（Verb）
　Exist as Material / Object / Essense ）
3. iru　: 居る　　 （Verb）
　Exist as Life Being）

How about this ?
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