1.What is Hinduism?Is it a religion?
It is an aggregate of various different practices in the subcontinent with the general current of "Dharma" running through them. Dharma can loosely stand for morality / righteousness. Following Dharma is something that moves us away from animals following "matsya nyaya" (law of fishes -- ie big fish eats small fish), and towards thinking about others.
There are various "forms" of Hinduism, as this is an aggregate religion. Over the years there have been various philosophies by thinkers (sadhus) and all of them kind of get clubbed into hinduism. In fact the charvaka school of thought was a "nastik" (atheist) school of thought, and that is also a form of Hinduism

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There were lots of local gods and dieties that people in different regions of the country worshipped, and these dieties while being part of the fringes of hinduism, kept moving in and out of the mainstream. All of these gods, dieties, and stories also get clubbed into Hinduism.
The time at which the initial Vedas were written, a lot of aggregation had already taken place, as you can make out by the references to some local dieties and gods.
2.What's the actual name of Hinduism cause "Hinduism" is a foreign name?
The core is Dharma. The root of the word Dharma is Dhr which means to hold tight. Dharma is something that holds the society together. The root word Dhr also gives rise to the word Dharti (i.e. earth -- something that holds us to the ground).
3.Do Hindus believe in the concept of heaven & hell?Do Hindus have prophets.
There is a concept of avatars, which is different from prophets. Some people believe that gods themselves came down in the form of various avatars, while others think that the avatars are symbols of the human journey across different yugas (eras).
Some people believe in a swarga and a narka (heaven and hell). But not all hindus believe in it.
4.How many dieties do Hindus believe in and which is the main one?
Infinite. You can keep adding/removing gods and dieties which appear to be dharmic as it is an aggregate religion.
Currently, there are 3 main gods and 3 main goddesses in the inner core of hinduism(Each god and goddess has certain symbolisms as you can make out by their pictures/idols by the things they hold, etc)
Gods: Brahma (creator), Vishnu (shiva), Shiva (destroyer)
Goddesses: Laxmi (wealth), Sarasvati (knowledge), Durga (emotion)
The ideal is that a person needs to have a balance of all three goddesses in their life in order to be "successful"
Ironically, Brahma the creator isn't worshipped as he is shown as chasing the three goddesses and signifies the chase without paying attention to Dharma.
Vishnu, accompanied by the snake (short vision) and a bird (long vision), signifies the ideal where the goddesses accompany him on their own accord, and he just follows the Dharmic route.
Shiva, the destroyer, indicates
Note that there are a lot more interpretations to each of the gods and goddesses, as each traditional depiction of a god has different symbolism.
5.How many different sects of Hinduism are there and what's their geographic distribution?
I wouldn't be able to answer this.
6.Are all Hindus forbidden from drinking alochol,fornicating and eating beef?
No. Generally speaking, harming animals for no reason would go against Dharma.
7.What's the most important book in Hinduism and do ordinary Hindus read it?and do Hindus fast like Muslims, if they do, how different is it?
Gita would be the most recent important book. A lot of hindus would've read some of it. The Vedas and the Upanishads (sort of a summary of the Vedas) are the oldest ones we know of.
Fasting: yeah some fast, but it is not necessary.
8.Do Hindus that follow different sects and worship different dieties believe they follow the same religion and believe in a body of "Hindu people", or do they see themselves independtly?
Most would consider themselves as "Hindu", though their own local dieties would be on a higher platform than the current inner core dieties.
9.What are some of the biggest sins in Hinduism, what are the punishments for them?
Adharma (opposite of Dharma) is the biggest sin.
10.What are non Hindus called?
There is no term for them, as far as I know.