Assets are the unique actuable IT resources around which we organize the elements. Please see more information in What is an asset. Usually it will be a host or common IT element which groups together other elements, like your internal infrastructure, domain names or just certificates.
At main Assets view you can get the main list of assets, domain names, groups used to keep them organized or locations where we guess they are located. If you have no assets or domain names found for your assets, start at upper right corner button.
If we found any domain name resolved to a given asset, it will be shown in the Asset domains tab, ready to be registered by you.
Once registered, domain names will be shown in Assets > Domains view: