API is an organization of petroleum companies - ExxonMobil, BP, Motiva, etc. Become employed by one and you can represent them and become involved. Otherwise, just come to the meetings, observe as a visitor, befriend some members, etc. If you find a committee or group you would like to participate in, apply for membership and get started. The API web site has meeting locations and dates. What is your interest? (tanks, valves, offshore, testing, piping, metering, etc)