Webex board can be deployed as a standalone SIP or H.323 endpoint however lot of its capabilities are gone.
So depending on the version of the device you can either provision the endpoint from the cloud or on-premises UC infrastructure.
If the version is greater than CE9.8.0, then the Webex Board can be provisioned from both cloud and on-premises infrastructure (CUCM, VCS and TMS). For more details on this refer to the following link https://help.webex.com/en-us/nwdhktbb/Migrate-Webex-Boards-from-Webex-to-On-Premises-Registration
For the Cloud provisioning: If you don't have your Webex Control Hub account created after you have purchased the licensing then you need to contact your account team from your partner or Cisco.
The registration process is really easy. Use the following link to guide you through this process: https://help.webex.com/en-us/n3hi0z8/Activate-a-Cisco-Webex-Room-or-Desk-Device-or-Webex-Board