When a model is Summoned to the game it is added to the Warband in addition to the models already recruited.
You do not need to pay the Rice Cost of a Summoned model.
Some models have Su as their Rice Cost, these can only enter play by being Summoned.
When a non-unique model is Summoned to the game it never has any Enhancement - Equipment cards attached to its card.
If a unique model that was recruited into the Warband is Summoned after being removed from the game, it retains any Enhancement - Equipment cards it was recruited with.