Starting from creation.
First Bhagavan makes Pancha-Bhootas (5 elements) from Prakriti (akasha/ether).
Then he gives life to Brahma. Then Brahma starts creation.
Lifetime of Brahma = 100 'brahma-years'. (not human years, as you'll see shortly)
1 Brahma-year = 360 'brahma-days'.
1 Brahma-day = 1 daytime + 1 nighttime
1 Brahma-daytime = 1000 chatur-yuga (...