Let's say a co-founder who worked (but no longer does) for a company prior to it going public still owns 1% (100,000 shares of 10,000,000 total) of the company.
If the company does an IPO and offers 25% of the company (2,500,000 shares) and gets $10/share, how would the ex-employee / co-founder that owns 100,000 shares sell those shares for $10/share?
What determines which 25% of the shares are sold and does that make the founders shares sellable on the market or other platform?