The first thing to do is spend time reading the actual Old Testament. One way to make that simpler for beginners is a good children’s Bible – If you are brand new to Christianity or are working with someone who is you might benefit from this as one of these will give you the major stories in order so that you get a feel for the flow of things.
Reading the Old Testament – Boadt
This is a good overall summary of things. It is quite thorough.
Getting Involved with God: Rediscovering the Old Testament – Davis
This is a book on understanding the genres of the Old Testament. It is the most basic book I have ever read on biblical genre and would be very, very helpful for someone who wants the basics to understand things better.
The Kingdom of God – Bright
Bright’s book was written back in the 50s and is a general, historical telling of the biblical story. It is a pretty quick read and puts the pieces together really well.
Contours of Old Testament Theology – Anderson
This book sounds more complicated than it is. Anderson’s purpose is to help you understand the Old Testament covenants. This is essential reading.
An Introduction to the Old Testament – Dillard & Longman
This is the most critical of all the books and still pretty conservative. They will give you the various major theories and let you sort it out. It goes through the OT book by book and gives you the basics.
I almost left one out that is the shortest of all of these and also one of the most helpful – Anderson’s “The Unfolding Drama of the Bible” – it helps you understand what the Bible is all about.
Most of these have earlier editions that you can get for a lower price used.
If you have a question about something more specific, say the life of David or the Pentateuch (Gen-Deut) please let me know and I will give more recommendations.
Last I have written a little bit about this and some of this may be of immediate help without buying anything:
Summaries of the Old Testament books – enough information without being overwhelming.
How We Got The Bible – a 14 page document outlining some information about the Old and New Testament, manuscripts, etc.