<p><strong>Register:</strong> If you have a virtual machine were you have already put all of the virtual machine files exactly where you want them, and you just need Hyper-V to start using the virtual machine where it is.</p>
<p><strong>Restore:</strong> If your virtual machine files are stored on a file share / removable drive / etc… and you want Hyper-V to copy the files to the appropriate location for you, and then register the virtual machine.</p>
<p><strong>Copy:</strong> If you have a set of virtual machine files that you want to import multiple times (e.g. you are using them as a template for new virtual machines) this is what you want to choose. This will copy the files to an appropriate location, give the virtual machine a new unique ID, and then register the virtual machine.</p>
<p>Source: <a href="https://social.technet.microsoft.com/Forums/windows/en-US/68aa2cbc-3386-44f5-aa87-b53c395d4b6c/hyperv-import-wizard-choose-import-type?forum=winserverhyperv">Technet forums: Hyper-V Import Wizard: Choose Import Type?</a></p>