Southperry's damage calculator - Magic damage.

In Maplestory, open up your stats window. Click the little arrow at the bottom of the stats window to extend the stats window to the right. Your magic attack value is located in the right pane (should be neatly labeled). Input that magic attack value with the INT value in the left pane.

INT is the stat you can allocate AP into. 1 INT gives you 1 MATK.

MATK = INT + MATK from equips + MATK from Meditate

Basic Attack is listed in the skill description