I was afraid it might not be obvious, I will update the guide later on. You need to collect power-ups to be able to use them, and you're only allowed to use them in specific glowing spots. We hope you give it another go soon and thank you for your kind words ;).

UPD: Thank you so much for giving it another go, as a designer I take full responsibility for that first drop. We were gonna add a short tutorial for it (you're not the first person who got stuck there) but in the end, we run out of time.