You can access the stock market once you perform an IPO (Initial Public Offering). You will be able to buy shares of other companies and other companies will be able to buy your shares.
The value of shares is determined by the share value (what a coincidence!). If the share value (‘SV’) of a company is $200, one share is worth $200. If the share value is $550, one share will cost you $550.
And this is how you make money: Buy low, sell high. If you buy 10000 shares of a company when their share value was $1 and sell those shares when their share value is $1000, you paid $10000 and got $10,000,000 – that means you made $9,990,000 profit.