Assuming you got GameFlow from the Unity Asset Store, installation into your project is easy.
The first time you use GameFlow on a particular computer, you will need to download it from the Unity Asset Store. For your first download and initial experiments with GameFlow, a new, empty project is highly recommended.
Go to the Window menu, and select Asset Store. Then, click on the My Assets button.
Scroll down to the GameFlow entry, and click on the Download button.
After GameFlow has been downloaded, click on the Import button. This will bring up the standard “Import Unity Package” window. Make sure everything is selected, and then click Import.
You should see the GameFlow assets in your Project window.
If you have an existing project, you can use the Asset Store to add GameFlow with the same process.
Once GameFlow has been downloaded, it will be available in the Unity Hub to be added to new projects via the the Add Asset Package button.
To make future updates easier, leave the GameFlow assets as a top level folder in your project - just leave them where they are to keep things simple.
Once you have installed GameFlow for the first time, you should go ahead and build a small test project to verify everything is working and begin to start working with GameFlow!
The update process is exactly like the installation: an update is simply a reimport on top of the existing assets.
Always read the release notes for the new version prior to updating to ensure that there are no breaking changes for your project!