To find resources on church history in the catalog, select the "Subject" search on the Advanced Search page. Some of the terms you would use include "Church history" or "Catholic history."
Depending on your topic, you can narrow down your searching even further by adding subdivisions. For example, under the "Church history" subject search, you could focus the search in these different ways:
Church history - United States
You could also change the results by the format of the book, adding terms like "Encyclopedias," "Handbooks, manuals, etc.," and "Dictionaries" to the end, bringing back just those types of items.
Broadening your search could be beneficial as well. Here are some general topics that could provide worthwhile books:
The Oxford Illustrated History of Christianity by 
The history of the popes from the close of the Middle Ages by 
The First Christian Centuries by BR- Christianity
BT- Doctrinal Theology
BX- Christian Denominations
DE- Greco-Roman World