Can someone explain to me what each of these variables do?

STR - I assume that this how much damage the basic attack does.
PDEF - i assume that this is how much you defend against from a basic attack.
ATK - i assume this is how much damage magic attacks do.
MDEF - i assume this is how much you defend against from magical attacks.
AGI - i know this is speed and how often you get to attack.
EVA - I know this is how often you can dodge/evade attacks, but is this for magical attacks too? and why does it start at 0 and never increase?
DEX - I have no idea what this is, but I assume this has something to do with magical attacks.
INT - I have no idea what this is, but I assume that this affects how much damage magical attacks do. but doesn't ATK already do that?

STR - The strenght of the player, as this increases, ATK increases too.
PDEF - has something to do with defence ... the more pdef, the less damage u receive
ATK - is the average attack an physical sttack do(this gets increased the higher your str gets.)
MDEF - the more you have here, the less dmg you will receive from magical attacks(fire, greater fire, mass fire ect ect)
AGI - speed the more speed you have, the more change you have to attack first.
EVA - your evasion.. the more you have, the more you evase.. this can increase by items perhaps(Selfmade items that is...)
DEX - How much the user's Dexterity affects the outcome of the skill. The higher the number, the more the Dexterity matters.(for evasing skills)
INT - int is for increasing magical skills(ATK is for physical skills)

This is a little incorrect. You can divide the stats in two categories: inherent stats and equipment stats.

Inherent stats
They raise by leveling up.

STR - Physical strength. Determine physical damage correction.
DEX - Dexterity. Determine the precision of physical attacks, and the critical hit chance. It has also the same effect as STR if used in skill damage calculation.
AGI - Agility. Determine the dodge rate and the critical hit evasion. It has also the same effect as STR if used in skill damage calculation.
INT - Intelligence. Determine magical damage correction.

Equipment stats
By default, 0. Only raise with equipment.

ATK - Physical attack. Determine the base damage for normal attacks and physical skills.
PDEF - Physical defense. Reduce damage caused by physical attacks.
MDEF - Magical defense. Reduce damage caused by magical attacks.
EVA - Evasion. Corrector value in dodge calculation.

thanks that helps a lot