The doctrine of the Trinity is part of systematic theology. Many Bible colleges can give you a decent grounding in the Bible, but often for systematic theology you need to read more deeply on your own. Again, I would recommend the above book chapter as a start.
@thoughtful has hit it on the nail here. Once you get deeper into the Trinity it is very easy to fall into heresy of one kind or another. (Remember this thread? A Conversation about the Trinity - #9 by dga471)