To download the community editor for State of Decay 2, you must visit the official mod page for it at the Nexus mod website.
At the nexus mod page for the Community Editor mod application, you will need to click files which should be the second tab below mod tabs and right of the mod description tab.
When you click files, you will need to click either slow or fast download depending on whether you have a premium nexus account. If you don't, just choose the slow download.
Doing so will start a download for the State of Decay 2 Community Editor mod application, and all you need to do now is wait for the mod to download.
Once downloaded, extract the zip inside the folder into a folder on your desktop for easy access. Click on the exe, and you will be able to use the State of Decay 2 Community Editor mod application to edit your current save game.
Just pick one of your save games from the save games listed in the app. However, at the time of writing, the Community Editor is currently out of date due to the recent Homecoming update or Update 26.
Because of this, you will need to wait for the Community Editor to get updated before you can use it to editor your current community in the game.
For more on State of Decay 2, check out our other awesome guides!