The following are links to William Lane Craig's YouTube videos on the doctrine of the Trinity during his "Defenders" Sunday school class. Just click on a link and it will open up a new browser tab to the video.
The following links are divided into three parts. 1. The Trinity, 2. The Holy Spirit, 3. Christ (part 8 begins the doctrine of the Atonement) ClickHERE for his lessons on the atonement.
Mere Christianity by C.S. Lewis is a classic book on Christian apologetics. There are a lot of things I disagree with in the book (including apologetical method), but I think the good outweighs the bad. Lewis includes a description of the Trinity in the book that is helpful in some respects. They helped me when I first became a Christian. Though, I realize now that the doctrine is much more nuanced than Lewis describes. Nevertheless, it can be helpful to those new to the doctrine. Because of that, and because Mere Christianity has been extremely influential in the 20th century, I've decided to post links to the section in his book that deals with the doctrine of the Trinity.