The world was savaged by the 4th great war. After the dust set, the planet was no longer capable of sustaining life. The people who have survived now try to make it through the days inside one of the lost bunkers scattered across the world. People are born and die in those claustrophobic spaces. This is their [small world] now.
You're not the first on this bunker. A lot of people have been here before, and a lot should arrive after you're long gone. That means you'll find a lot of scrap/parts all over the place. Assign people to scrap those parts so you can build useful stuff with it.
People need food to survive. Build industrial ovens and assign someone to operate it to turn parts into food. Don't worry about where it is stored. People will simply consume them from time to time if available.
Same as food. Water can be gathered using hi-tech water wells, which also needs to be operated by someone.
Most objects need energy to run. You can generate energy building power plants. They run on their own, so just make sure they're actually working.
You managed to bring 4 people to the bunker. More should arrive as the day passes. But the world is actually getting worse so they'll come in worse conditions later on, if they come at all...
Each person has four stats: Health, Food, Water and Sleep.
As long as the bunker has food and water, those numbers will stay topped. If there is no food or water, they will drop. If they reach zero, the person dies.
Doing stuff tires them. When the sleep number fall to ~25, they'll try to find a bed to sleep. If no bed is around and/or available, they'll sleep where they are.
Health will drop a little each day. This is a dying world, after all. If it reaches zero... you know what happens.
You can assign people to do some stuff.
The first and most common action is Scrap. That will make the person wander around collecting parts.
The second action is Cook. If there is an available oven, the person will move there and start cooking.
The third action is Pump Water. If there is an available water well, the person will operate it.
The fourth action is Fix Stuff. Objects may break over time, use this to order a person to fix them.
The fifth action is Heal Up. If there is an available medical center, the person will go there to heal.
The last action is Sleep. This will make the person drop anything it's doing to take a nap.
As told before, doing stuff tires people. A person will automatically go to sleep and then go back to work when waking up. People ordered to fix stuff or heal up will also return to their previous tasks if they were doing something before.