>>72847196the Fate series is generally about (usually) seven mages having a death battle for the Holy Grail (which can grant any wish) by each summoning a Servant (the spirit of a legendary hero or character from history e.g. King Arthur, Hercules, Gilgamesh etc.) and the Servant is in one of seven classes based on their combat style (Saber, Archer, Lancer, Rider, Caster, Assasin, Berserker)
the Servants and their Masters all fight to the death which involves teamups, betrayals, using Command Spells (a limited number of commands that the Servant is forced to obey) etc.
Almost every entry into the series intentionally has it where the rules get bent and subverted as it goes along and there's more convoluted bullshit really going on behind the initial premise - also most spin-offs like this game diverge from the basic premise by having extra classes, rogue Servants and other deviations
the only real constants are that Saber (Artoria, the blue one) and Gilgamesh (smug golden asshole) are the strongest Servants, the Archer class insists on using any weapon other than actual bows and most Sabers can shoot lasers from their swords