Food is hard to come by deep under the earth. By far the most plentiful ecosystem is the warm, freshwater sea accessible from the bottom of the rift (A crack in the earth many thousands of feet deep, one of the busiest, most bountiful, and most dangerous places below ground, this will make a little more sense once you have a map) The albino whales, deep water seals, and blind fish that live here provide a bounty to all that can make the long and dangerous journey to this heavily fought over territory, but a resource far more valuable was found here. Giant anglers with translucent skin and clear, glass-like teeth didn't seem very appetizing, but the light from their lures was enough to allow plants to grow, and these continue growing long (for between two and four months) after death.
This provided the basis of the dwarven food system. A bat colony is killed, and glass angler lamps are hung in the cavern. A few hardy plants can then grow in the waste the bats left in the bottom of the cave. In addition to what fishing can be done and a few carnivorous plants that a grown to provide a more diverse diet. Sometimes a hunting party can return with a few seals or even part of a whale. In leaner times, alternate meat sources are sometimes found...
Time is hard to measure without a sun or stars. Generations and harvests are the main way time is measured. For shorter periods, candles taller than your average dwarf are placed throughout most settlements, lines or notches marking off the hours as the candles burn down. You're better off not asking what the candles are made of in most cases...
Factions: Background on the Deadstone Dwarves, Rock Gnomes, Myconids and Raiders will be up soon