A concordance is a book that lets you search for a word/concept in the Bible, Koran, or other religious text. Here are some concordances UD has:
New Strong's Exhaustive Concordance (to the Bible): Reference Collection, call # Ref BS 425 .S8 1995
Oxford Companion to the Bible (e-book; includes listing of Bible passages plus explanation of each concept)
A Concordance of the Qur'an: Reference Collection, call # Ref BP 133 .K37 1983
Looking to read up on a topic, idea, or theme? Credo & Britannica are perfect places to start. Keep in mind that current topics most likely won't be inlcuded, but religion-related topics have been around for quite some time. The encyclopedia articles in these databases will give brief overviews of topics. If you are brainstorming ideas for your paper, these will help.
If you are focusing on an idea that is related to your hometown (such as your church), you might want to try looking at your local newspapers and/or news sources.
Keywords are simply those words you type into the search box to get the results you want. Just like in Google, you don't type your whole question, just the important words or terms that will help you get the answers. Remember to consider synonyms when you create your keyword list.
So what are subjects then? Subjects are a specific word or phrase some librarian has assigned to a particular topic. Basically it's a tag we attach to articles or books. Why would we do that? Because that way when you search for that specific word or phrase you get EVERYTHING that has been tagged with that term. You can find these subjects (or subject headings) in the library catalog and most databases (except JSTOR). Usually they live along the left side bar or in the middle of the record (when you click on a specific book or article).
Want a real life example of keywords? Let's look at nicknames and Facebook. Let's say a bunch of your friends decide to upload photos on Facebook. Now each of these friends calls you by a different nickname. So they tag you in them by whatever they call you. In order to see all of these pics, you'd have to search for each of your nicknames to find them.
Subjects on the other hand are like your actual given name. Or at least your Facebook official name. Now when you actually tag photos on Facebook, you know you're forced to tag them with their "actual" name. And while it may be less personal or descriptive, you do get all the photos of you when you use the offical name tag.