Instants, Activated Abilities both go on the stack. The stack gives players the opportunity to respond to spells/abilities before they resolve. The stack is a First In Last Out (FILO) zone, where spells and abilities exist until they resolve or are countered.

Do you control a creature on the stack?

Only objects on the stack or on the battlefield have a controller. Objects that are neither on the stack nor on the battlefield aren’t controlled by any player. Effects that deal with cards in the graveyard would refer to their owner.

Does taking control of a creature give it summoning sickness?

Yes, a creature gets summoning sickness after taking control of it. 302.6.: A creature’s activated ability with the tap symbol or the untap symbol in its activation cost can’t be activated unless the creature has been under its controller’s control continuously since their most recent turn began.

Can you use creature abilities during opponent’s turn?

Activated abilities can be activated at anytime you have priority (in other words: when you could play an instant) unless they state otherwise. Do be aware that you have to tap the creature BEFORE it is declared as an attacker.

When is an ability not a triggered ability?

That’s it, really. If the ability doesn’t have one of those three words, it’s not a triggered ability. Note, however, that some keyword abilities, such as Flanking, are triggered abilities, even though those particular words don’t appear on the face of the card.

How does soul Warden’s triggered ability work in magic?

Soul Warden’s ability does not resolve immediately. Just like spells and activated abilities (such as Prodigal Sorceror ’s damage ability), triggered abilities use the stack. This means both players get a chance to respond to them before they resolve. But how do we know that Soul Warden has a triggered ability?

Is the earth elemental a triggered ability in magic?

It isn’t a triggered ability, so there isn’t anything to trigger. The turn isn’t over yet (the end of turn step is still part of the same turn), so the effect doesn’t wear off and Earth Elemental is still 8/5. Adam realizes that he has Fling in his hand, and decides to Fling the Earth Elemental at Barry.