When you go to your brokerage account and buy a share of Google, you aren't buying it from Google, you're buying it from some other random shareholder out there who wants to sell. Google does not see a cent of that money.

In general, the only times a company gets money when you buy shares are if you participate in an IPO, or if an already-public company decides to offer more shares for sale in order to raise some money, and you buy some of those shares. (There are exceptions, but retail investors like you and me usually don't get invited to participate in those deals, though.) The vast majority of shares that trade hands on the markets every day are not owned by the company whose name is next to the ticker symbol.