A Group Program Agreement allows the organizer of the group program to set up the expectations for the group members from payment to general organizational rules. No negotiation is happening in this document - it's a one-sided agreement, created by the organizer.
An online group or organization can use this document when they want to accept a new member. The document can be used by different online groups or organizations, regardless of size.
A Membership Agreement is a document used in cases when the member becomes a regular patron of the other party, either a group or organization.
Bylaws are mostly the rules for how the organization will be governed and they describesmany of the non-profit's activities, such as the composition of the Board of Directors, voting, and annual meetings.