They can move around the map at your command, exploring and conquering new territory. Units may also be used to defend your territory and communities. They serve solely as a defensive force. These are individual characters which may lead units. The leader adds bonuses to all units in its group and in the same hexagon.
Realms begin with only one leader, called the realm character.
Once attached, items adds bonuses to that unit and all other units and leaders in the same hexagon. Only a few communities belong to your realm at the start of the campaign. These are described in the Set-up Report you have received and are shown on the map in the report. Communities provide both wealth and new units. You may invest in it to bolster its economy, or conscript units from it, which weakens its economy.