1. The Grail is the crystallization of a highly concentrated amount of Prana that acts as both the key and doorway to the Throne. Now thats simply taken from the clan submission but it basically means the Grail and by extension the Throne is practically composed of prana which is a place all surgebinders are linked too basically. Prana manifests differently for each user typically depending on the faction they are apart of, fallen being red or black etc. Typically prana isn't able to manifest in the real world but they use the Surgebinders as a portal to appear in the real world.
2. Surgebinders are basically servants of the grail and are portals for prana to appear in the real world as I said before. Surgebinders have practically limitless possibilities when it comes to controlling and manipulating prana. Surgebinders typically gain usage to prana by being exposed to it by an existing member, such as how Galahad found he could make more Surgebinders by continuously placing his Knights in the throne and repeating this over numerous days.
3. The Surges are as follows, Surge of Evocation which is the most raw and unrefined surge of the group, it is typically in an energy based form and whatever it touches is transformed into more of the exact same energy, this is supposed to be the most destructive to the world around it surge compared to the others as it is much more unrefined and controlled. The next surge is the Surge of Armament which is basically the NP genre of Surgebinders, it allows the user to call forth prana-enhanced objects such as weapons or armours that are permanently stored in the throne. These noble phantasms practically cover anything ranging from swords, bows, ships etc. These objects contain a large amount of raw Prana inside allowing the object to possess unique abilities. The abilities and objects of this Surge are practically limitless and can be anything that the user can imagine. Surge of Augmentation serves as a way to enhance techniques or living things through prana but cannot be applied to objects which imo is pretty lame. This surge doesn't supply new abilities merely enhances existing ones for example you could use this Surge to travel at 2x speed but once it ends you suffer a similar penalty to the benefit you gained. This surge can also exist to weaken techniques as well for example causing the user's own fire technique to be cooler or a wind techniques wind be less violent. Finally for the C O O L ! Surge of Transcendence, this surge is basically an opposite of the surge of armament where as instead of summoning weapon or objects to the field they summon themselves, opponents, allies, or anything else to the Throne itself. The user gathers a crazy amount of prana in their body and releases it over the surrounding area which travels at 3x the user's movement speed (now idk if this means current moving speed or base moving speed). This allows the user to bring people into their own reality marble but something to note is the prana released to those that are not surgebinders is not harmful to them unlike in Surge of Evocation. But the Reality Marble is essentially a world of the user's own making and they have complete and utter control of the entire world that they are in, being able to manipulate things with simple hand gestures or mental commands. The Reality Marble is essentially the ultimate technique of the Surgebinders and is only able to be made by those HS rank or above and need to be submitted as pccj prior to use.