Hey there, thank you for the feedback!
Mhmm I was unsure if I should post the "F to use" control hint in the first level already, because it only gets relevant at the second and succeeding levels.
In the first level, the only thing you need to do is to find where the shadows of the two large spikes align (they should land on a pile of rocks) and then press E (E is to use the invisible teleporter for the next level and F is to use other objects that are found in later levels)