First of all, start with a skeleton. Then put some flesh on the bones. Then fatten it up. And all the time pray God to send life into it! But remember, a living skeleton is better than a handsome corpse.
Evangelical Press are publishing a series of short paperbacks by various authors on several of the major Christian doctrines. These are simply written, and easy to understand. These will give you the bones, and a little bit more. So will G. I. Williamson's two paperbacks on The Shorter Catechism (Presbyterian & Reformed Publishing Company). And I cannot recommend too highly Derek Prime's Questions on the Christian Faith answered from the Bible (Kingsway Publications), which I have on my desk, and have used, as I have written each chapter of this book. I would never be without it.
To put a little flesh on the skeleton, next read The Westminster Confession of Faith by G. I. Williamson (Presbyterian & Reformed), and that most excellent summary of the Christian faith, In Understanding be Men, by T. C. Hammond (Inter-Varsity Press). How I thank God that this book came into my hands almost at the very beginning of my Christian life.
You will then know enough to be able to choose what books will be best for you after that. I must especially recommend The Confession of Faith and Outlines of Theology by A. A. Hodge; and Systematic Theology by Louis Berkhof. All of these are published by the Banner of Truth Trust, and I have used them extensively over the years, and very particularly in the preparation of this little book. I am happy to acknowledge my deep debt to them.
Best of all –join a church where the Bible is explained week by week by a minister who is filled with love for the triune God, and who does all that he can to develop the spiritual life of his congregation!