The SMPTE Standards Workspace is provided by Kavi Corporation (and you will hear the Workspace referred to as "Kavi"). Once you have been registered for Standards Participation you will be able to log in to the Workspace. (SMPTE has a Single-Sign-On system, so if you are already logged in on the main smpte.org site you will not be required to log in to the Workspace (unless your login has expired).
The Workspace provides a hierarchical structure of Groups, each providing a document repository, email list, calendar, balloting, etc.
At the top of the SMPTE engineering committees structure is the "Standards Community". If you have just registered for standards participation, your first task is to join the Standards Community. Select "Join Group" and carefully read the Participation Agreement. If you agree to these terms, complete the click-through process. You are now a member of the Standards Community, and may join additional committees (groups) without further formality.
However, you need to understand that the structure is hierarchical. To join a sub-group, you must be a member of its parent. So, please start by reviewing the list of the top-level Technology Committees, and join the one(s) that interest you. You can review the list, and see a synopsis of each committee's work area at Technology Committees.