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How are shares used, and what are they, physically?
Shares used to be paper documents, but these days they are more commonly held electronically instead, although this partly depends on what country you're in. But it doesn't make any significant practical difference. Regardless of their physical form, a share simply signifies that you own a certain proportion of a company, and are thus entitled to receive any dividends that may be paid to the shareholders. To sell your shares, you need a broker -- there are scores of online ones who will sell them for a modest fee. Your tax forms are entirely dependent on the jurisdiction(s) that tax you, and since you've not told us where you are, no one can answer that.