There is one God who is Father, Son and Spirit. Simple.
The concept of the trinity – one God in three persons – is both stunningly simple yet astoundingly complex. But more importantly, it is foundational (and I would argue that it is paramount, even) in terms of understanding anything about who God is and what he does.
There are many great books (Delighting in the trinity by Tim Chester, plus the relevant chapters in Doctrine by Mark Driscoll, Knowing God by JI Packer and Christian Beliefs by Wayne Grudem), web resources (such as the section on 'Trinity' at theResurgence.com) and other resources (listen to 'Three in One' from the God Unlimited album for something a bit lighter!) that we can turn to in order to engage with the doctrine of the Trinity. However, the best place to go to understand God is in his word, the Bible.