Your colonists need somewhere to live in. Homeless colonists sleep on the ground but will slowly lose happiness and even health, if they're exposed for long. Having enough shelters for everyone is a top priority. Tents and houses not only improve their Happiness but also shield them from the elements. Without a bed to sleep on, colonists will get Tired and eventually Exhausted due to lack of sleep, and they can also get Sick, requiring medical attention.
Shelters range from simple two-person Tents all the way to (circumstances considering) comfortable Houses. Upgrading to sturdier houses improves people's Happiness and provides better protection against the harsh conditions and even Catastrophes and disasters. They also encourage your populace to have children as they feel more secure and private in a proper home. Colonists move to the closest available shelters to where they work, so spreading out housing reduces the time people walk back and forth.