kb:importing standardized formats [Zotero Documentation]
The most popular formats are RIS, Bib (La)Tex, and MODS. If you have a database stored in one of these formats, such as a BibTeX database you've compiled or a RIS database you've exported from another reference manager, you can import them into Zotero by clicking File → "Import…" and choosing "A file". See also Moving to Zotero .