Conjurers are offensive spellcasters who specialize in violent and volatile Conjurations. Relative to other magical backgrounds (such as the Wizard), they begin the game with a lower general Spellcasting skill, but have a higher Conjurations skill to compensate.
Some species may receive different items based on their unique restrictions.
These are adjusted by your species' aptitudes.
Conjurers have two main advantages over Wizards: a more powerful Magic Dart at the start of the game, and guaranteed access to mid-game nukes in their starter spellbook (Bolt of Cold and Freezing Cloud). Early on, Mephitic Cloud helps neutralize many powerful threats, which is necessary as they do not get access to Blink without finding a lucky early book. In most cases, they are confined to a "stand and nuke" approach for solving all situations until their spell repertoire expands.
Unlike the various Elementalists (who can also be "blasty"), Conjurers start with no elemental magic skills. This makes them a good choice for less experienced players who want to try a blaster, but aren't yet sure what (if any) type of elemental magic best suits them.
See the following guides:
Prior to 0.9, their starting spell book was different, most notably lacking Mephitic Cloud.