Monster origins
Monsters in Final Fantasy VIII live on the moon, and fall to the planet at regular intervals known as the Lunar Cry. The monsters breed between Lunar Cries and increase their numbers, and some animals are also mutated into monsters when the Lunar Cry occurs. The Lunatic Pandora is a machine designed to artificially cause the Lunar Cry, using the Crystal Pillar.
 Monster Details
Monster encounters are random; but they can be cut down by junctioning Diablos' Enc-less ability to an active character, or completely avoided altogether with Enc-none. Bosses and certain battles aren't affected by the Enc- abilities though. After catching and naming a Chocobo, you can use it for transport and speed past any monsters to avoid encountering them on the World Map.
Additionally, all monsters except bosses can be turned into cards using the Card command, and those cards can then be used to play Triple Triad to win more cards; or they can be refined into items using Card Mod.
Using Scan on a monster reveals it's strengths and weaknesses.
Information on the many monsters and enemies of the FFVIII World can be found in the Bestiary.