Schedule items can be assigned to groups. An item can be assigned to a group at the time of creation or afterwards. An item can only be assigned to an existing group. Until assigned a group, an item is listed as "Unfiled." Unfiled is not literally a group but a statement about the item's group status.
To assign an item to a group at creation, select the desired group from the "Group" drop-down menu as you are filling in the fields on the item editing page.
To assign an existing item to a group, please see "Moving Schedule Items."