Let me try again, otherwise look at a GameFAQs walkthrough: the final boss battle against Ares has several phases, each separated by a cutscene. The end of the first phase is triggered by a QTE initiated when Ares has the "circle" icon over his head after being weakened enough. Go up to him, press "circle", and the QTE starts. Press the required button, Kratos will strike Ares, which gives him a bunch of red orbs and makes a second button prompt pop up. If you push it, that ends the first phase of the battle. If you don't push it, Ares will hit you and you can weaken him once again to unleash those red orbs, infinitely... Better?