Enchanted creature can't attack or block, and its activated abilities can't be activated.
Whenever a creature enters the battlefield under an opponent's control, you may attach Prison Term to that creature.
5/1/2008 The last ability works only if Prison Term is already on the battlefield. You may move it from the creature it’s currently enchanting onto the new creature.
6/8/2016 Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text.