The Canadian Pony Club operates at three basic levels: local, regional and national.
Your particular club is a local "Branch". It is likely run by a parent committee comprised of a DC (District Commissioner - a title carried over from the English roots of Pony Club), an ADC (Assistant District Commissioner), a Secretary and a Treasurer (or in smaller branches these last two roles may be combined). This is your executive or decision-making body for your club.
You may also have other positions in place such as a Youth Rep (a young member who represents your membership on a regional board), and perhaps a Testing Rep (who organizes regularly scheduled testing when appropriate). As branches grow, other roles may come into play along with committees. You may be asked to participate in one of these roles at some point. It is important to note that horse knowledge is not a prerequisite to being on a committee or executive. A number of these roles are more administrative and organizational in nature. Don't be afraid.
The one exception to this is a Pony Club Centre. This is an established riding facility which has requested and received authority to offer the Pony Club program to its members and it is run by a representative of the stable and other volunteer parties.
This group of people is made up of representatives of all the Branches in your Region or designated geographic area. There are 13 Regions nationwide and each has a Regional Committee with an executive much like the local one. This group oversees the running of broader training and competition opportunities for all clubs in the region, as well as higher level testing. It acts as an intermediary between local branches and National Head Office, disseminating information up and down in both directions.
The National body of Canadian Pony Club is tasked with setting policy, remaining abreast of issues and information in the broader equestrian world, national budget handling, and protection of the values and integrity of the club in general. It has an elected Board and a Management Committee to oversee the day to day running of the organization. It is the final authority on policy, rules, discipline etc.