Groups are a (configurable access control) feature available within professional and enterprise plans. 

See "How do I upgrade from a free plan?" if you need to upgrade. 

Groups (e.g. HR, Finance, Marketing, Project X, London, Paris etc.) are a powerful organizing construct that facilitate the management of access control across your Method Grid account. 

By creating groups, you have the ability to assign access permissions (to folders and grids) at a group-level. 

On switching to a professional or enterprise plan from a free plan, system groups are automatically created for the three base member roles i.e. architects, builders and users. Changing a member's base role, thereafter, will switch the member to their new base role system group i.e. system groups are automatically updated. Similarly, when moving from a free account to a paid account, all pre-existing members are treated as "Internal" and added to the Internal system group; thereafter members can be assigned as "Internal" or "External" and the related system groups update automatically. See "How do I invite and manage external members into my account?"

See "How do I add a new group?", "How do I configure access to a folder?" and "How do I configure access to a grid?"