The Stagger Gen data pack needs to be present in the same world as your data pack for its functionality to be available to your data pack.

The functions in the #stagger_gen:overworld/new_chunk and #stagger_gen:nether/new_chunk function tags are executed once per second per chunk in the 9x9 chunk area around every player that is currently moving between chunks (which one is executed depends on which dimension each player is in). These functions are executed positioned at Y0, with the lowest x and z coordinates within the given chunk.

The functions you add to either of these tags will need to check whether your data pack has already generated within a given chunk, and record the fact that they've generated. This is done with NBT data on an item in a barrel at the bottom of the world within each chunk; e.g. for my Underground Overhaul data pack I use the following command to check if it's already generated in a given chunk, and if not, to call all its world generation functions for a new chunk: execute if block ~ 0 ~ minecraft:barrel unless data block ~ 0 ~ Items[​0].tag.under_over run function #under_over:new_chunk . Underground Overhaul also records that it's generated in a chunk with the following command: data modify block ~ 0 ~ Items[​0].tag merge value {under_over:1b} , which simply adds a boolean nbt value to the item in the barrel for later checking, but you could store more complex data if you want to track which features of your data pack have generated in a given chunk, or which version it was that generated in a given chunk, or any other data about the chunk you might want to track.

Stagger Gen also comes with a few functions to help you place structures or world features in the Overworld (although they can be used in any dimension). These functions are meant to be executed as a placeholder entity so you can summon your marker entity, run the desired function to move it into position, and then execute at the entity to place your structure or feature. The functions, and their effects, are as follows;

• stagger_gen:overworld/find_surface will move the marker entity to the highest block in the world at the current x & z coordinates, but will ignore trees and plants (i.e. it will place the entity underneath trees, if there are any at its x & z coordiantes).

It is recommended that you use the spreadplayers command if you want to randomise the x and z coordinates of where your structure/feature will generate. It can also be used to find caves in 1.16 with the new "under" condition.