Spell Tiers
All spells and wands as well as some other items in wizardry have a tier. Tiers are a measure of power: the higher a spell or wand's tier, the more powerful it is. Conversely, higher-tier spells and wands are much rarer than those of lower tiers. There are four tiers: novice, apprentice, advanced and master, each being more powerful than the last.
Novice
A wizard's journey to mastering the arcane begins with novice spells. Novice spells are ubiquitous: they can be found almost everywhere and most wizards know nearly all of them, even if they don't usually use them. It is fairly easy for a non-wizard, given a wand, to learn novice spells, and this makes them the place to start for aspiring wizards. There are relatively few novice spells, mainly because they are rather simple - an apprentice level of magic is required to cast spells that are any more complex.
Apprentice
Apprentice spells are a step-up from novice spells, both in power and complexity. Most of an adept wizard's staple spells will be apprentice level, as they provide a good balance between effectiveness, fairly low mana cost and short cooldown times. Apprentice spells are much more numerous than novice spells, and encompass a wide variety of utility, attacking and defensive abilities. A certain level of practice is required in order to use apprentice spells effectively, though they are fairly readily available if you know where to look.
Advanced
Advanced spells are where the really impressive magic begins. A wizard who knows advanced spells is not a challenge to be taken lightly, and will have spent years training their magical skills in order to cast them. Advanced spells are, in fact, the most numerous of all the spells, mainly due to their diversity. However, they are also considerably rarer than novice and apprentice spells, so expect to do a fair amount of exploration to find them.
Master
Only the most powerful wands are capable of channelling the power required to cast master spells. Master spells often require a significant fraction of a wand's mana in order to cast them, and can have cooldowns of 30 seconds or more. In return, however, a master wizard is able to cast the most powerful spells in existence. The combination of their immense power and incredible rarity makes many master spells the stuff of legend - master spell books are often priceless relics from the ancient past... or at least, almost priceless. It is said that some wizards are prepared to offer their most powerful spells to those they trust, for a price befitting of their rarity.