how do you pronounce dyr?
Similarly to the English word 'deer'
When do you use en and when do you use et? Whats the difference?
You use 'en' for masculine nouns, 'et' for neuter words and 'ei' for feminine nouns. The difference is the noun's gender, which has to be memorized.
Would et be for category nouns? Such as child and animal?
No, there are no such categories. The gender a noun is assigned is quite arbitrary, and will have to be memorised with each noun. It does not match up with biological gender, and the only rules that exists are for certain categories of loanwords.