There are many articles about agile. The principal methodologies used are Scrum and Kanban.
The Agile has started from a Manifesto (document) : https://agilemanifesto.org/Here is a good article to understand Scrum with the main keywords and ceremonies:
https://www.visual-paradigm.com/scrum/from-small-teams-to-scaling-agile/
Going futher ?
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