Look at the top five cards of your library.
ExileTo exile an object, move it to the exile zone from wherever it is. See rule 406, “Exile.” (CR 701.13) one of them face down and put the rest on the bottom of your library in a random order. 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) the exiled card without paying its mana cost if it's an instant spell with mana value 2 or less. If you don't, put that card into your hand.