- Phoenix Guides - This is one the best ways to get started. The guides cover most of the fundamental topics and explain the ins and outs of how Phoenix works. I would start here and look up the parts of Elixir you don't understand as you go.
- Programming Phoenix - Still in beta, but very well done. I would recommend getting it even while in beta. It has a brief introduction to Elixir and covers all the important concepts in Phoenix
- Elixir Getting Started Guide - This is the official Elixir getting started guide. You don't need to know everything here to get started, but it covers a lot of fundamentals in sections 1-21.
- routing - Covers the router and pipelines
- plug - Plug is used almost everywhere in Phoenix. This is a good intro to what it is and how it works.
- ecto - Covers changesets, migrations, etc. Very helpful to get started with.
You'll find that the documentation for Phoenix, Ecto and Plug are quite good. Here are some pieces of documentation that may be particularly helpful when getting started
- Phoenix.ConnTest - Covers testing controllers
- Phoenix.Controller - Covers using controller functions like render, redirect, etc.
- Ecto.Repo - All the ways you can interact with the database (insert, update, query)
- Ecto.Query - How to generate queries
- Ecto.Changeset - How to cast and validate data in changesets