Well simply put.
 A basic stax deck works by powering out cards like chalice and trinisphere and tangle wire to "lock" your opponent out of the game until you get active smoke stax plus crucible of worlds to eat away their permanents.
A basic fish deck works by using cheap disruption like null rod force daze stifle to hurt the opponents development. Then using cheap disruptive or udercosted creatures like meddling mage kataki and grunt you beat face till they die.