I did not understand how to play at first. What's the connection between the numbers of the clues and the placement on the board? The example has the following

I did not understand how to play at first. What's the connection between the numbers of the clues and the placement on the board? The example has the following clues: ACROSS 1.Common breakfast drink 3.Not in operation 5.Underground resources 7.Chinese capital 9.Faculty of perception But the grid is 5x5