Shared bibliography entries live in bib/references.bib (see myst.yml).
In MyST Markdown you can cite with standard roles once keys exist in that file, for example:
{cite}`lamport2002`
{bibliography}Add only sources you actually cite in the chapter text. Prefer persistent identifiers (DOI, stable URLs) in BibTeX entries.
For informal background, inline links are often enough; reserve the bibliography for works you treat as evidence or essential further reading.