A stock becomes available for public purchase through the process of an initial public offering (IPO). This is when a company decides to raise funds by offering shares of its stock to the public for the first time. Investors can then purchase these shares and become part owners of the company. This is a significant event for a company, as it allows them to raise capital and potentially grow their business. As an investor, it is important to understand the implications of an IPO and how it can impact the stock's value and your investment.