There are many other systems of magic in our world, but the Holy Grail—[ with a gesture to. the stone he's sitting in ]—has its own system of magic.
To put it simply, every sixty years or so, the Holy Grail will choose a number of mages to participate in a War against each other. The winner is granted one wish to any degree of impossibility.
In this War, the weapons that are used are not spells, but summoned familiars—those who made an impact on human history, no matter how slight, are capable of being summoned as one of these familiars, known as Heroic Spirits. These classes are generally based on what sort of weapon we are known to use in life, and in a regular Grail War, there are seven standard classes. You would know them as divided between Knights and Cavalry.
With each class comes their own strengths and weaknesses—naturally, humans are far more capable than fitting into a specific type of person; for example, it's more likely than not that a person well-known for riding a chariot can also use a lance or other weapon, but in these Wars we are given a specific skillset based on that specific part of our myths. It's a balancing act, you could say, with a clear hierarchy of which classes are "better" and which classes are "worse".
Knight classes are considered better capable of fighting, as they have more allotted strengths, and Sabers are considered the best out of the Knight classes. The Cavalry classes exchange strength for alternative skills—for example, Assassins are not typically strong, physically speaking, but they are able to use Presence Concealment, being completely undetected by anyone and everyone, magical and not.
[ pause ]
In other words, it's basically like a game. Because it's like a game, even in its being a War, there are classes with stats and skills. However, it's also most certainly a War, as there is great and immeasurable power behind every Servant summoned, and even just one Servant could wipe out a city should they so desire it.
Re: 『Heaven's Grass』
To put it simply, every sixty years or so, the Holy Grail will choose a number of mages to participate in a War against each other. The winner is granted one wish to any degree of impossibility.
In this War, the weapons that are used are not spells, but summoned familiars—those who made an impact on human history, no matter how slight, are capable of being summoned as one of these familiars, known as Heroic Spirits. These classes are generally based on what sort of weapon we are known to use in life, and in a regular Grail War, there are seven standard classes. You would know them as divided between Knights and Cavalry.
With each class comes their own strengths and weaknesses—naturally, humans are far more capable than fitting into a specific type of person; for example, it's more likely than not that a person well-known for riding a chariot can also use a lance or other weapon, but in these Wars we are given a specific skillset based on that specific part of our myths. It's a balancing act, you could say, with a clear hierarchy of which classes are "better" and which classes are "worse".
Knight classes are considered better capable of fighting, as they have more allotted strengths, and Sabers are considered the best out of the Knight classes. The Cavalry classes exchange strength for alternative skills—for example, Assassins are not typically strong, physically speaking, but they are able to use Presence Concealment, being completely undetected by anyone and everyone, magical and not.
[ pause ]
In other words, it's basically like a game. Because it's like a game, even in its being a War, there are classes with stats and skills. However, it's also most certainly a War, as there is great and immeasurable power behind every Servant summoned, and even just one Servant could wipe out a city should they so desire it.