Adding citations from online resources (databases/websites) is the most efficient way to build your zotero library. Zotero will automatically detect when you are searching in most databases or other online resources and provide an address bar icon to easily add citations to your Zotero library. If an icon does not appear in your address bar for some reason, you can generally use the database's export function to export the citation as an RIS.
Zotero Browser Icon Examples:
If the metadata does not import automatically, you can add the information manually: