This is the 2nd most frequent Slovak word.
na
"Na" in Slovak means "on" or "onto."
Here, 'na' is used to indicate movement towards a specific event or location (concert).
Idem na koncert.
I am going to a concert.
In this context, 'na' indicates a location on a surface (wall).
Obrázok je na stene.
The picture is on the wall.
Here, 'na' expresses the purpose or the goal of the preparation (exams).