If you are looking for a deeper understanding of the doctrine of Faith Alone, a great way to start would be to study Scripture (all of it). Special focus on Romans and Ephesians will bring great clarity. Additionally, the documentary American Gospel: Christ Alone provides a lot of clarity. The documentary goes to great lengths to bring clarity to the gospel, contrasting both ancient and modern false teaching with biblical teaching on the truth of the Gospel.

Additionally, here is a link to several resources on the topic from the Gospel Coalition.