Installation
Natsura is a plugin: it loads into Houdini rather than replacing it. Setup offers two ways to do that, and you can have both.
The Natsura launcher is a shortcut, named for your Natsura version, that starts Houdini with Natsura loaded. Your normal Houdini stays as it was, so Natsura never gets in the way of other plugins or a studio pipeline, and each version sits in its own folder with its own shortcut. This is the recommended way.
A package install uses Houdini's package system: a small Natsura.json file in Houdini's packages folder that tells Houdini where Natsura is. Natsura then loads every time you start that Houdini version normally. Setup can write the file for you, or you can write it by hand.
Each Houdini licence has its own Natsura download, so check which one you need first. See Commercial Use and Activation & Licensing.
Commercial Use
What you need to use Natsura commercially. Natsura is a Houdini plugin, so your rights depend on both your Natsura licence and your SideFX Houdini licence.
Install Natsura (Package Method)
Install Natsura by hand with Houdini's package system on Windows, for when the setup script doesn't fit your environment.