For example, they say "Put in 1, 4 and 9th sector"?
They don't say that. They say "Put in neighbors 1, 4 and 9".
It is assumed that the "neighbor" is a bet on the wheel track, the standard width of 5 numbers. The size of such a bet is taken as a multiple of 5 chips, since the central number is automatically covered, 2 to the left and 2 to the right (+/-2).
A $5 bet on neighbors "1" covers 16-33-1-20-14 at $1 on each number.
There are extended neighbors (+/-4) and narrowed neighbors (+/-1), but this is specifically stipulated. In Evolution roulettes, it is convenient to independently adjust the width of your bets in neighbors.
What other sectors are there?
If we consider a "sector" as a block of numbers on a field or track, then the division and breakdown must be taken from the context of the narrator.