Share classes are the different types of shares that a corporation can issue to its shareholders.
A corporation can have a single class of shares, or it can have dozens of highly customized share classes. To differentiate share classes, they are usually listed in alphabetical order (Class A, Class B, etc.). "Class A" shares won't necessarily be more valuable or powerful than "Class B" shares. It all depends on the description of each share class.
The corporation's standard shares are called Common Shares. Corporations often choose to have one class of Common Voting shares and another class of Common Non-Voting shares. Each common share represents an equal fraction of the corporation, but only the holders of the Common Voting class will be able to vote on issues relating to the corporation's business.
More complex share classes are usually called "Preferred Shares." These shares are often added for tax-planning purposes on the advice of an accountant. Despite being called "preferred", these shares won't necessarily have more value than Common shares.
To learn more about the specific characteristics of Common and Preferred Share Classes on Ownr, read here.
The corporation's initial share classes are included in the Articles of Incorporation. New share classes can be added at any time by amending the Articles of Incorporation and informing the government of the change, all of which can be done directly from your Ownr account.