In the Institutes, God separates out our natural knowledge of God as Creator and revealed knowledge of God the Redeemer.
His basic idea is that we have an in-built, instinctive awareness of God (sensus divinitas) which is not dependent on logical arguments or examination of the world around us. A good quote to use here may be: 'There exists in human minds and indeed by natural instinct, some sense of Deity, we hold to be beyond dispute.' (Insititutes)
Calvin's concept of 'knowledge' can, I think be split up into two distinct ideas. The first being his sense of Divinity.
A good start to a paragraph, in my opinion, would be to quote the bible. A good one that sums up everything we are going to say: 'For what can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse.' - Romans 1:19-20
For Calvin the whole point in doing theology (although he did not like that term) was to gain wisdom that we might live for the glory of God.
God has revealed himself to us in creation. Each human being has a sense that God exists, the sensus divinitas.
But what about the people who claim not to believe in God? Or those who believe in other religious ideas? Calvin, unfortunately has a rather harsh outlook upon these people. (To get top marks you will have to discuss limitations of Calvin's ideas, and so this may be a very good one to use!) In his eyes, when we sin, we distort and suppress the witness of the sensus, but a sense of God cannot be totally eradicated from the human heart.
This means that at the end of the day, we know enough to be held accountable for our unbelief and idolatry. However, according to Calvin, all is not lost! God can still redeem us, for he is revealed through scripture. The way that scripture is revealed is through prayer- indeed, for Calvin, prayer was ‘the chief exercise of faith’ Institutes, and the fundamental expression of Christian piety. Knowledge of God as a redeeming figure is also found when we look at what the Bible says about Jesus (remember, Cavin thought that the Bible was the absolute word of God and everything that was written in it was the exact word of the Holy Ghost). If we look at Jesus' story Vhristians may see that God saved them through the death of his Son, to reveal the depth of his grace and love. This is the redeeming God.
Another aspect of Calvin's ideas on knowledge may be the concept that nature is a witness to God's power. In other words, knowledge of his greatness is 'revealed' to us through nature. Again, it is always best to use a Bible quote here to show that you are basing your ideas on real theological ideas; a good one is 'God’s power and divine nature are clearly seen since creation, being understood from what has been made' (Romans 1:20). For Calvin, if we witness a beautiful sunset or go to the grand canyon and see how vast it is, we can infer from these sights the power of God. This quite close to Aquinas' Design argument. A limitation of this concept might be that surely the power of nature is just as much a testament to the greatness of evolution as it is to the power of God?
As such, we have 3 clear concepts, that would fit nicely into 3 paragraphs for an essay. To get the best marks, memorising quotations, and criticising theological theories is very important!