Shareholders are the owners of a company. The ownership of a company through shares is one of the principal benefits of incorporation – it permits an almost endlessly customizable ownership structure. Shares can have many different types of attributes – such as voting, dividend entitlement, participation upon company sale / windup etc. which are beyond the scope of this FAQ.
The share structure of a company and the distribution of shares can change an unlimited number of times over the lifespan of the company, however it’s best to consult your accounting and legal advisors prior to making any adjustments and to ensure that the appropriate documentation is in place. Many entrepreneur duos “handshake” to split shares 50/50 and then never actually distribute the shares … no big deal until there’s a disagreement or the company starts to succeed.