Some private companies are privately held, but many are publicly traded.
Have you ever seen a stock certificate? Privately held stocks are often actually handed to you. They are neat.
While all publicly traded stocks in the USA are technically owned Cede. Cede has all the certificates in vaults in NYC, and we buy and sell the rights to those stocks. Rights that are almost never exercised.
Anyway, a privately held company is only allowed a limited number of investors, and does not have any price discovery, so is not interested in small investors. Apple, Amazon, Exon, etc. will allow almost anyone to buy a share on the stock market. But a privately held company is not interested in your money.