In the campaign, factions raise armies of units, which move around the campaign map and battle other armies, or take settlements. Here on Total War: Warhammer Wiki, each faction's page has an infobox on the right hand side, showing key information. On the campaign map, players can click the button in the top right corner of to view the faction summary screen which displays information about their faction. A few factions (such as Warherd of the Shadowgave prior to the Silence and the Fury DLC) only appear in multiplayer.
Most factions may be seen in the campaign, though which factions appear will differ depending on the campaign.
The faction summary screen for Itza faction of the Lizardmen race.