Create a folder on your hard drive or network share
Download the Office 2016 Deployment Tool from the Microsoft Download Center.
Execute the Deployment Tool and install it in the folder you created.
Create a .xml with the following: (edit path)
Full overview of the Office Deployment Tool.
Run the following to download the offline installer:
[path]\setup.exe /download [configname].xml
Run the following to use the offline installer:
[path]\setup.exe /configure [configname].xml