You may
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) Aura and Equipment spells as though they had
flashFlash is a static ability that functions in any zone from which you could play the card it’s on. “Flash” means “You may play this card any time you could cast an instant.”
Multiple instances of flash on the same object are redundant. (CR 702.8).
Whenever an Equipment you control enters, you may
attachTo attach an Aura, Equipment, or Fortification to an object or player means to take it from where it currently is and put it onto that object or player. If something is attached to a permanent on the battlefield, it’s customary to place it so that it’s physically touching the permanent. An Aura, Equipment, or Fortification can’t be attached to an object or player it couldn’t enchant, equip, or fortify, respectively.
If an effect tries to attach an Aura, Equipment, or Fortification to an object or player it can’t be attached to, the Aura, Equipment, or Fortification doesn’t move. If an effect tries to attach an Aura, Equipment, or Fortification to the object or player it’s already attached to, the effect does nothing. If an effect tries to attach an object that isn’t an Aura, Equipment, or Fortification to another object or player, the effect does nothing and the first object doesn’t move.
Attaching an Aura, Equipment, or Fortification on the battlefield to a different object or player causes the Aura, Equipment, or Fortification to receive a new timestamp.
To “unattach” an Equipment from a creature means to move it away from that creature so the Equipment is on the battlefield but is not equipping anything. It should no longer be physically touching any creature. If an Aura, Equipment, or Fortification that was attached to an object or player ceases to be attached to it, that counts as “becoming unattached [from that object or player]”; this includes if that Aura, Equipment, or Fortification leaves the battlefield, the object leaves the zone it was in, or that player leaves the game. (CR 701.3) it to target creature you control.