You can buy stocks and shares of a particular company by first finding yourself a stock broker who helps you invest your money into the specific company you desire shares for.
Ultimately, the money goes to the previous owner of the stock which can be a company, group, or individual. However, the money passes through different hands depending on how the shares were bought...
You can buy one share of stock, however commission costs range from around $5 to $13 per transaction. So, if you buy one stock for $50 and the commission to buy it is $10, that's a 20% expense....
Yes you can buy most anything online. Alot of people go online every minute to buy all kinds of different stuff. The Internet is probably the most used thing in the world.