The Ancient Christian Commentary on Scripture is a line by line interpretation of the Bible by ancient Christian Fathers of the Church. Organized by modern scholars, it excepts commentary on specific books, chapters, and verses of the Bible and places them alongside the actual Biblical text. Many of the excerpted works have also been published in the Fathers of the Church series, so you can potentially cross-reference what a particular ancient commentator is saying about a particular line of the Bible with one of their sermons on the topic.
The Ancient Cristian Commentary on Scripture is comprised of multiple volumes of commentary for both the Old Testament and the New Testament, as well as a volume dedicated to the Apocrypha. Each volume covers a specific portion of the Bible (e.g. Volume I of the Old Testament series covers Genesis 1 to 11). To use the volumes, simply find the volume that corresponds with the line(s) of scripture that you are studying, find the range of lines in the upper right-hand corner of the page, and consult the corresponding commentary. It may also be useful to consult the general introductions that are included in each volume, as these will help place your lines in the greater context of that particular Book.