Choose target creature you control and target creature you don't control. If you
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) this spell during your main phase, the creature you control gets +1/+1 until end of turn. Then those creatures
fightA spell or ability may instruct a creature to fight another creature or it may instruct two creatures to fight each other. Each of those creatures deals damage equal to its power to the other creature.
If one or both creatures instructed to fight are no longer on the battlefield or are no longer creatures, neither of them fights or deals damage. If one or both creatures are illegal targets for a resolving spell or ability that instructs them to fight, neither of them fights or deals damage.
If a creature fights itself, it deals damage to itself equal to twice its power.
The damage dealt when a creature fights isn’t combat damage. (CR 701.14) each other. (Each deals damage equal to its power to the other.)