On the official website you also can find the section "Arnulf can help" or the like. There you can find a link to download a demo-video of the game such as an animated walkthrough.
But if you want to play through the game on your own: If you have arrived the state, where the girl's pussy is open for your caressing, don't finger inside, but only be careful in caressing the outer upper range of the pussy, near below her clit click on the right side, hold and move down outside and release, repeat about three or four times, until you see a veneric drop coming out. Then double-click strongly on her face and wake her up. Then she will be ready for fucking!