Calvin isn't bothered with idle speculation about the nature of God:
Let us then willingly leave to God the knowledge of himself [which we shall do] if we conceive him to be as he reveals himself to us, without inquiring about him elsewhere than from his Word (Institutes, I.xiii.21).
So, in chapters 10-13 of Book I of the Institutes, Calvin is keen to open the Scriptures to us and show us God, as he relates to us as Creator (God as Redeemer is the subject of Book II). And in so doing, Calvin isn't concerned to fill our minds with lists of attributes and the like, but
the knowledge of God set forth for us in Scripture is destined for the very same goal as the knowledge whose imprint shines in his creatures, in that it invites us first to fear God, then to trust in him. By this we can learn to worship him both with perfect innocence of life and with unfeigned obedience, then to depend wholly upon his goodness (I.x.2, emphasis added).
Perhaps this practical emphasis on fear, trust, worship and dependence explains why chapters 11 and 12 are devoted to the subject of idolatry and dishonourable practices in worship? Scripture, in speaking of God, prescribes that "nothing belong to his divinity is to be transferred to another", and Calvin saw that happening in his day, in the way images were being used and honoured in the context of worship.
Chapter 13 is devoted to the doctrine of the Trinity, which is fundamental to our understanding of God. This is a subject I've grown to love in recent years, largely through hearing or reading things by Mike Reeves, Ellis Potter and others (if I'd have read their books, I'm sure I could have added Sam Allberry and Tim Chester to that list). But I have to say I found Calvin's treatment quite heavy going. There were evidently plenty of controversies in his day about the Trinity, and a lot of the (39-page) chapter is devoted to those. Nonetheless, Calvin gives a clear articulation of the what we mean by "Trinity",
that Father and Son and Spirit are one God, yet the Son is not the Father, nor the Spirit the Son, but that they are differentiated by a peculiar quality (I.xiii.5).
(That's "peculiar" as in "distinctive", by the way.) And he describes the distinction between the three Persons as follows:
to the Father is attributed the beginning of activity, and the fountain and wellspring of all things; to the Son, wisdom, counsel, and the ordered disposition of all things; but to the Spirit is assigned the power and efficacy of that activity (I.xiii.18).
(It is possible to see these distinctive characteristics of the three Persons reflected in the way that everything in the world exhibits identity, relationality and movement through time, as Jeremy Ive does in his fascinating thesis, drawing on the work of Herman Dooyeweerd and Dirk Vollenhoven.)
The remainder of Book I looks at how this Triune God relates to the world, as its creator and sustainer.