First you need to create an account at www.ilok.com and download their iLok License Manager software. Install it on your computer. Second, register your plug-in on eventide.com, which will automatically send a license to your iLok account. Make sure to install the plug-in into your computer. Intallation files are located on individual product pages and on the Downloads page.
Alternatively, for products that allow computer authorization, after you've installed iLok License Manger and registered the plug-in, you can launch your DAW. Once the DAW scans the installed plug-in it will present a dialog box to install the license on your computer or iLok.