In MTG what is a creature spell and does islandwalk clify?

I have a card that has islandwalk my friend has a card that blocks target creature spell my understanding of spell is something you have to tap mana/creature to achieve, consequently she believes her card should block islandwalk i have been playing without my card for arguments sake but is islandwalk a spell, activated ability or what i would like very much to put my card back in my deck one way or the other i just want to be sure i'm playing by the rules