timing of selection

[chocoman]

is there a general rule or keywords on cards that make clear when your obliged to select/target something at activation or at resolution?

 

[Digital Jedi]

Generally, when the first sentence states something like "Select X Monster" and is a stand alone sentence, it's an activation selection. Selections that are part of a resolution are generally incorporated into the later part of the text. But it's a very general rule that doesn't always apply. But we usually have a ruling or Judges List message letting us know if it doesn't follow that basic rule. Creature Swap, for example, is a little vauge and appears to break that general rule, but there's a ruling that let's us know.