This question should accept the following answers, at least
I want a mango.
I want the mango.
I want mangoes.
I want the mangoes.
All of these can be valid translations depending on the context the Hindi sentence is spoken.
In a language like Hindi, you simply use the singular form of a noun to describe the general idea of the thing. In English we tend to generalize using the plural form, so a statement like "I like cats" in other languages might be "I like cat", or "I want mangoes" might be "I want mango". Some languages that use articles will attach an article, and this occasionally happens in English, like "The lion is a majestic animal." Even in English this sentence has practically no difference in meaning from "A lion is a majestic animal" or "Lions are majestic animals".
What is the difference between "mujhe aam chaahie" and "main aam chaahati hoon"? What "tense" is the verb chaahana in when it is "chaahie", and why do you change main to mujhe?
I always was under the impression that chahtaa= want and chaahiye = need. So if one says main seb chahtaa hun, it means I want apples. And mujhe seb chaihiye means "I need apples". My family is from Mumbhai and this is how the distinction was explained to me.
According to my Urdu language booklet (by Assimil, in case you know this publisher):
Noun + चाहिए = want or need sth, depending on the situation (e.g. मुझे चाय चाहिए = I want/need tea);
Infinitive Verb + चाहिए = need or have to do sth (e.g. तुझे भारत जाना चाहिए = you need to go to India);
Infinitive Verb + चाहता/ती/ते + होना = want to do sth (e.g. मैं चाय पीना चाहती हूँ = I want to drink tea).
I hope that helps, that there is no mistake and that these structures are also used the same way in Hindi.
As per my understanding, there are 2 types of subjects in Hindi: natural and grammatical. When the grammatical and natural subjects are the same, we use "main" (or any other personal pronoun). Conversly, when the grammatical and natural subjects are different, we use "mujhe" (or any other such pronoun: tumhain, aapko...).
Let's compare 2 sentences: 1) Main aam khana chahti hoon. (I want to eat mangoes.) 2) Mujhe aam chahiye. (I want mangoes.)
In both sentences, the natural subject (= the doer of the action) "want" is "I", as reflected in the English translations. However, in Hindi, "I" is only a grammatical subject in the 1st sentence, hence the use of "main". The 1st sentence can be transliterated as "I (main) - mangoes (aam) - eat (khana) - want (chahti hoon)".
On the other hand, the grammatical subject in the 2nd sentence is "mangoes", not "I". Thus the 2nd sentence can be transliterated as "By me (mujhe) - mangoes (aam) - are wanted (chahiye)".
You can compare this to the active and passive structures of English, for example "I read a book" and "A book is read by me". In both cases, the doer of the action of reading (the natural subject) is "I", but in the latter sentence, the grammatical subject of the verb "is read" is "a book", not "I".
NB: I hope this explanation was clear enough and correct. That would be great if a more knowledgeable person or a native could check my reply.
Let's take example of money with "need" and "want."
"I want money." or "I need money."
If you have money before the context arises then you want money otherwise you need money.