It's actually a very clever structure! Please open the following image to follow along as I elaborate:
https://pbs.twimg.com/media/F_PGOPOacAApU8e.jpgAt the top level, there is the non-profit board of directors (i.e.: the ones Sam Altman had that big fight with). They are not beholden to any shareholders and are directly bound by the company charter: https://openai.com/charter
The top-level nonprofit company owns holding companies in partnership with their employees. The purpose of these holding companies is to own a majority of shares in & effectively steer the bottom layer of our diagram.
At the bottom layer, we have the "capped profit" OpenAI Global, LLC (this layer is where Sam Altman lives). This company is beholden to shareholders, but because the majority shareholder is ultimately controlled by a non-profit board, it is effectively beholden to the interests of an entity which is not profit-motivated.
In order to raise capital, the holding company can create new shares, sell existing shares, and conduct private fundraising. As you can see on the diagram, Microsoft owns some of the shares in the bottom company (which they bought in exchange for a gigantic pile of Azure compute credits).