This is the 2nd most frequent Russian word.
на
"На" – on, in, at, onto.
Here, 'на' indicates a location or position, meaning 'on' in English, showing where the book is placed.
Я положил книгу на стол.
I placed the book on the table.
In this sentence, 'на' is used to express a means of transportation, translating to 'by' in English.
Мы поедем на автобусе.
We will travel by bus.
Here, 'на' denotes a location or place, meaning 'outside' or 'at the street' in English, describing an outdoor condition.