Evocation spells manipulate energy or tap an unseen source of power to produce a desired end. In effect, they create something out of nothing. Many of these spells produce spectacular effects, and evocation spells can deal large amounts of damage.
For a list of all spells which are of the school of Evocation, see: Category:Evocation spells.
Evocation is never able to be chosen as an opposition school by any wizard meaning these spells are always available to all wizards. This means there is little need to discuss the pros and cons of the entire school in case you could choose to have it as an opposition school. Evocation's opposition school is Conjuration.
The main point of Evocation is damage, although some spells are different such as Darkness and Light. Damage spells are more useful to a Sorcerer who has both a more limited selection of spells (so should take advantage of instant metamagic such as Empower to use a wider variety of spells in different slots at times), than to a Wizard who can specialise in different areas as and when - going from someone who casts primarily will-based holding and paralysis spells, to necromantic death spells after a single rest.
Generally damage also is only very useful against low level creatures, especially when the caster is part of a party or group, since when in a group the main people who deal damage should be the fighter, barbarian and sneak attacking people, since they have unlimited attacks, while a single fireball, once cast, cannot be recast. A fireball also can easily be saved against, while a swing of a sword, once connected, cannot.
The damage output of fighters is much much higher in the long term than mages. A mage who uses protective, and ability enhancing spells on the fighters can make fights a lot easier with less resting (which is not always possible), or can provide backup spells to hold, fear or slow the enemy creatures, making it easy work for fighters to finish them off.
Another highly effective way to use a wizard in the official campaign is to memorize a few "save or screwed" spells such as hold person, bigby's crushing hand, mass hold monster, fear, etc. to eliminate a few foes at beginning of a battle. Then, direct damage spells such as chain lightning, fireball, Issac's greater missle storm, cone of cold, etc., can be used to weaken remaining enemies while melee characters can finish off the additional weakened and remaining foes. Although the only potential downside of this approach is that it requires frequent resting, this is easily done in the official campaign.