There are two main ways to populate your EndNote Online library with references, manually or upload of records from databases:
Search the database via the web interface as you normally would. Select the references you want, then save or export them. Every database works a little differently. Some offer an obvious EndNote export, like Web of Science:
And some offer a more generic RIS export (like Scopus):
Most databases can export to EndNote with these general steps:
Export References from PubMed as an .nbib File
4. Choose options for citations
5. Download file
Importing Citations to EndNote Online