The boilerplate needed, the first metadata title, link, description and the many additional optional values.
Dates in RSS conform to RFC 882

Each RSS feed has items. Each feed can contain the entire content, unabridged, or a summary of the content and that it should be read on the site.

Atom is XML-based but is a little bit stricter and more finely specced than RSS.

JSON feed is the newest format discussed around. It has similarly.

RSS can be auto-discovered with the link tag in HTML.

Gotchas:

• use absolute URLs for media in the RSS feed. RSS Readers can be disconnected from the origianl domain.
• escape HTML entities in XML or use CDATA wrappers.
• Web-based RSS readers have CORS rules to follow. Setting an Access-Control-Allow-Origin: * is mandatory header on your XML/JSON files ensures these web-based clients don’t get blocked by security policies.
• the readers have limited display
• validation via the W3C Feed Validation Service or the JSON Feed Validator.

Read the RSS 2.0 Specification, the Introduction to Atom, the RFC 4287: The atom syndication format or the JSON feed version 1.1 Explainer.