Who sells the shares?

In any market, we need someone who sells and someone who buys.

In the share market, if you want to buy shares of company A, you need someone who is ready to sell them to you. This is someone else like you sitting somewhere else, probably in a different city.

If we buy 10 shares of company B, someone else sold 10 shares of company B.

If we buy 10000 shares of company C, someone or a group of people sold 10000 shares of company C.