Once you have selected your preferred product variant, you can start working with Capture One. You get the option to either use that as a trial for 30 days, buy a license from the Capture One online store, or activate it with a license key that you have purchased already.
Capture One typically requires an internet connection for software activation. However, it can be activated when offline if necessary (anyway, an internet-enabled device, such as a smartphone or another computer, is still required to generate an activation key). For more information, see the section on offline activation. Capture One Pro DB does not need an internet connection for activation.
This guide describes Capture One for Apple® Macintosh® and it is also applicable to Capture One for Microsoft® Windows®, though some specifics are not listed.
If you would like to change the activation mode after some time, read this article for more details.