Web Users can belong to one or more Web User Groups. A Web User will adopt the permissions from any Web User Groups they belong to. They will also have access to any folders which the Web User Groups are authorized to access.
The Groups tab is split into two columns. The column on the left displays the available Groups to which the Web User does not belong. The column on the right displays the Groups in which the Web User is a member. Click to highlight groups and then use the direction buttons between the columns to move Groups to the appropriate side.