Current scientific thought holds all things in the universe to be made of four elements; fire, water, earth and air. While it is not common knowledge the learned hold there is the fifth element cosmos that determines the form the other four elements will take. It is cosmos the magic user manipulates threw various means, reshaping matter to his will. Needless to say this not easy, even worse, this theory was not arrived at by scientific observation so it is not even consistent so exceptions abound.

Magic System Design Sheet
What Powers  are allowed in the campaign

Inner Magic
Magic from the castor's own power. The Hermetics

Transient Magic
Magic gleaned from the natural forces of the world. Alchemists and the like

Granted Magic
Magic done the easy way; get something else to do it. Priests and witches.

Mana Reserve
Spell casters are allowed to create external Mana Reserves they can tap for spell casting
Sample objects and the reserves are;

Wizards Staff       10
Shinny Scull Cap       4
Wizards Robes with occult embroidery      3
Wizards Robes with Ming the Merciless Collar    5
Dribbly  Candles       2
Crystals      2-9
Meteorites      6-36
Stuffed Alligator        8

Familiars

Any Magic User player character is allowed to have a familiar as follower. See Fantasy Hero Source Book page 74 for more details.

True Names

Magic User's  MANA is assumed to have the Advantage Usable By Others built into it for free.  Masters typically require their students to tell them their True Names. (see page 74 in the Fantasy Hero Source Book for more details)

Shared Magic
(see page 50 in Fantasy Hero Companion II)

 
From a Normal to a Magic User
There are certain rituals that cab set up the Normal's MANA to be used by a specific Magic User  much like the True Name.  In game mechanic terms the character buys their EGO with the advantage Useable By Others or the Magic User must cast a transform on the Normal that will allow this.

To a Magic User from a Normal
Magic Users may only take mana involuntary from a normal with a Transfer or Drain spell.

Magic User to a Magic User
This Is allowed but only by touch. Note: that with the True Name issue any Non Player Character Magic User short of a follower will be unwilling to do this with a Player Character

Magic Users Combining Powers
Is allowed as described
 

Dwarves - Dwarves exclusively uses the Runes, see transient magic.

Elves - Elves are rather magical and use the Collage of Fairy Magic. They are only required to take Concentrate, Incantations, Gestures, and Side Effects disadvantages on their powers. The only draw back to this for an Elf is for every 10 active points in spells they have must take 5 points of the Physical Disadvantage: Vulnerability "Cold Iron". Small wonder then those naughty Elfish Enchantresses are leery of the peasant farmers and his lawn shears?

Ehgans - Work like humans for magic, though Ehgans typically use granted magic.

Rawmian - Like humans

Ursc - Use rune magic like dwarves.

Pertinent Occult Languages

 Chaldean
 Old Bothian
 Borean- (a must!)
 Hebrew
 Yhule
 Magic User's Own Secret Code