i have caught pets in battle and they had spells they put on my pets but when i got them they didnt have them. how do i get and use magic spells like poison, ect?

You get them by spending your pets proficiency points in their proficiency tree.

Every time your pet levels up by 5 levels, they get one proficiency point, which you can use in their proficiency tree (click proficiency, under spend level ups, in the pet profile). Each proficiency tree is after a certain element and will give extra bonus to the pet. At 5 proficiency point, it will unlock the "magic spell". So your pet needs to be at least level 25 to have one.