In Frostpunk, you don't only focus on your own city. Sooner or later, you will have to send special units outside your city to search for additional resources or new people who can work.
This is the most basic goal. Beacon can be unlocked at early stages of the game - thanks to it you will be able to create your first scouting team. You can do that by clicking on the building. Its screen informs you about requirements that you have to fulfill in order to create a scouting team (press the button to create a new team).
This unlocks the world map with markers. Each marker is for a location that can be explored by your scouting team. Click on a marker and then on a scouting team. This displays a button that allows you to travel to that place and shows you an estimated time of this journey.
After that you can go back to your town. Progress of that team is displayed in the upper right corner of the screen. Go back to the world map once they reach their destination and select the right scouting team. This opens a report which informs you about results of that expedition. You can see what has been discovered in a given place. Sometimes, you will have to make decisions, e.g. escort survivors to your town or leave them.
Scouting is a good way of getting additional resources. This option also allows you to keep getting new citizens which leads to development of your town. Because of that you should invest in a scouting team as fast as you can.
The game lets you establish depots that will provide your city with additional resources: coal, wood, food and steel. After establishing them you will receive a certain amount of one type of resource once per a specific period of time.
However, to establish a depot you need to reveal a suitable location first by sending your scouting team. This can happen during a regular expedition. The game informs you when your team discovers a place like that - besides a marker, you will also see a symbol of a resource that can be gathered in that place.
You need a specific team to establish a depot. You can do that by unlocking Outpost Depot in the technology tree. These teams are created in the same way as scouting teams.
Once you have a team, you can open the world map and order that team to visit a location suitable for establishing a depot. After reaching that place you can decide to build a new depot. From now on caravans with a specific resource will travel to your city. If you want to close a depot simply open the world map, click on its marker and select the option to close it.
Depots are a great solution when you have problems with getting enough supplies of a given resource. Each caravan delivers enough resources that will eliminate problems with having small amounts of them.