IV's are a number from 0-31, that adds extra points in a certain stat at level 100 depending on the number in the stat.
Let's say a Oddish at level 100 without any IV's will have:
HP - 100
Atk - 100
Def - 100
SpAtk - 100
SpDef -100
Spe - 100
Say those are the stats at level 100 without any IV's. Meaning 0 IV's. Than if a different Oddish had 31 in everything. The Oddish with 31's would have:
Hp - 131
Atk - 131
Def - 131
etc...
You can't "IV train." As IV's are given to a Pokemon when they are caught, or picked up. And they will stay the same no matter what.