Leader Character
You directly control a single character that can be used to: organize and assign followers, use items and abilities, attack directly, and place buildings using Resources.
You have a limited Health pool and when it runs out you will have to wait a short time to respawn at the Crystal.
Health and Attack Power can be increased, along with unlocking new abilities by spending Aether to level up at the Crystal.

Followers
Followers can be appointed to perform various tasks, such as combat roles, gathering Materials, and healing injured by selecting them and then assigning them to the appropriate building.
They have limited health, and if they die they're gone for good.
They also have levels and traits which differentiate them, these can be viewed on the Followers Info menu.
Followers will arrive every day as long as your population isn't at its cap. This cap can be raised by building houses.

Resources
Materials: Acquired using followers assigned as gatherers at a Harvester building. Gatherers can harvest Materials from Ores, Trees, and various other objects.
Aether: Primarily acquired from defeating enemies.
Relics: Usually dropped by tough enemies or alike. When hauled back to the Crystal using followers it will be automatically collected.
Food: Food is acquired by building a mill and assigning followers to it. Food is required to sustain a population, without it people will starve.

Crystal
The Crystal is the heart of your settlement; if it is destroyed the game will end. 
The Crystal allows you to level up, it will attack nearby enemies, and will also heal nearby injured.

Threats
Threats come in the form of enemy raids, usually at night. Enemy structures can also appear on the map and cause small raids even during the day. 
Some enemies can only be found during the day and can be defeated for valuable Resources.
The number and difficulty of threats will increase with the growth of your population and the passing of time. 