I was reading the rules for Using Magic Items and there is a part which just isnt clear to me in how it works.
2nd last paragraph, just before size and magic items:
Unless stated otherwise, activating a use-activated magic item is either a standard action or not an action at all and does not provoke attacks of opportunity, unless the use involves performing an action that provokes an attack of opportunity in itself. If the use of the item takes time before a magical effect occurs, then use activation is a standard action. If the item's activation is subsumed in its use and takes no extra time use, activation is not an action at all.
When you need to activate a magic item, most tend to be a standard action, but some are not. How can you tell/know when the magical effect is suppose to occur? Yes most items to mention what their action cost is, but its when creating new ones that dont have that built in description.