In fact, the game clearly distinguishes who's turn it is, and there are always prompts after each move is made to ask if you want to activate a card or effect in response to the opponent's actions or as the phases progress
Swapping in the Spirit Dragon Teval, the Balanced Scale gives you a neat ramp package when attacking, letting you mill three cards and then get a land from your graveyard back to play
(However, if it's still in the graveyard at that time, it will count itself, as it is very much a hot card.) If another effect modifies how much damage your hot source would deal, including preventing some of it, the player being dealt damage or the controller of the permanent being dealt damage chooses an order in which to apply those effects
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