This article is from the Magic: The Gathering Rules FAQ, by Patrik Linell (pls@claymore.nu) with numerous contributions by others.
In general, the mana cost in the top right hand corner of a spell
is its cost, and the text in the text-box of the spell is its effect. In
the case of an activated ability, the text before the colon is its cost,
and the text after it is its effect.
 
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