Notification is about advising people who may be affected by the application of agrichemicals that spraying activity is about to be undertaken. These people may be neighbours or occupiers of nearby sensitive areas (e.g. schools).
You should have identified the people you need to notify - and their contact details - when you prepared your Spray Plan.
The rules around notification differ between Regional Councils, so check your council's Air Plan for details. For example, some regional councils do not require you to notify your neighbours at all while others require you to notify them if you are using a motorised spray, but not when you are using a knapsack.