I would recommend you learn about ArchiMate by studying the resources below.
Official ArchiMate 3.0.1 specification by the Open Group. This is the official ArchiMate specification written by the Open Group. It details everything related to the ArchiMate Enterprise Architecture modeling language, such as the notations, semantics, relationships, viewpoints, etc.
Book - Mastering ArchiMate Edition III. The is one of the most popular books that talks about ArchiMate. It gives an introduction to the ArchiMate language as well as to show you key aspects of successful enterprise modeling, along with many different patterns for practical use. Although the aim of the book is to teach the language, it also provides necessary background, making it suitable for readers with levels of knowledge (even if you are not familiar with the language). Besides ArchiMate, also covers subjects like virtualization, bitcoin/blockchain, BPMN, infrastructure as code, processes versus functions, SOA/API, ESB, Terminal Services, etc.
Guide - Full ArchiMate Viewpoints Guide (Examples Included). Viewpoints is an important concept in ArchiMate. A viewpoint contains a dedicated set of ArchiMate elements that allows architect designers to model a specific aspect of an enterprise architecture. The official ArchiMate 3 specification provides 23 ArchiMate example viewpoints for architecture designers to follow. This ArchiMate viewpoints guide goes over all these 23 ArchiMate viewpoints, with clear description and ArchiMate diagram examples for each of them.
Article - What's New in ArchiMate 3? This article provides an overview of the ArchiMate 3.0 Specification which is a major update to the ArchiMate 2.1 Specification and was published as an Open Group Standard in June 2016.
Article - What is ArchiMate? This article introduces ArchiMate , an independent modelling language for enterprise architecture, invented by the Open Group.
Hope this helps.