The Game Concepts in Civilization VI.
As you continue to play Civ 6 you'll run into some unique gameplay concepts, namely the idea of Housing in your cities, or how Food works for your Citizens. For example: Each of your cities has a "housing limit" that can be understood as a cap for your population. When a city's population reaches the number below the housing limit the city starts to change, growing 50% slower, and once the housing limit is reached, it will grow even slower and stopping or declining soon after.
To increase your Housing you'll need to have access to fresh water by building your city next to Rivers, Mountains, Lakes, Oasis or by building an Aqueduct. Whenever a Settler is selected, the non water tiles in the map will be marked as one of the 4 colors: Red, Grey, Light Green or Dark Green, showing you the best options for water in which to place a new City Center.
Amenities is another one of the basic Game Concepts which contributes to what make cities grow. Amenities work similar to happiness in previous Civilization games since Global happiness has been removed and replaced with Amenities, and is now one of the the things that make the people "happy", but are more at a local level.
So now for each 2 Citizens in a city you are required to have 1 Amenity (excluding the first 2 Citizens). A Civilization's Capital starts with a single Amenity by default from entertainment, but additional cities will each start with 0 amenities and require 1 when the 3rd Citizen has been reached.
There are 6 ways to get positive amenities: luxury Resources, Civics, entertainment, Great People, Religion and through the building of National Parks. Adversely, there are 2 known ways to get negative amenities: War weariness and Bankruptcy. Each Luxury Resource gives +1 Amenity for up to 4 cities. Luxury resource allocation is currently a bit unknown at this point,but it has been said that in larger cities it is automatic and the cities which need the most number of luxuries receive more.
Science: Science is accumulated per turn, as dependent on all sorts of things throughout the game, Buildings, Wonders, Great People, as well as Tile Improvements, Natural Wonders and a few other things. Various Technology is researched when enough science is accumulated, depending on the Era you are in, or the Tech you are researching.
In regards to Science, the Technology tree is similar to previous Civ games with a major addition: the Eureka! bonus, which can be seen as a sort of quest. Once you meet the requirements the Technology becomes 50% easier to research. Note that if a tech is already under research and you fulfill the requirements and get a Eureka! bonus in the middle of it, depending on how far along you are, you push it an additional 50%, and if you're more than 50% already, the tech gets pushed to completion.
Culture: Like Science, Culture is also accumulated per turn, and there is a new "Civics tree". Advancing throughout the Civics tree allows you to unlock new forms of Government and opens new Policy Cards, which you can slot in and out of your Government "deck" for specialization purposes and the layout changes based on the government type you pick. Policies come in four variations: Military Policies, Economy Policies, Diplomacy Policies, and Wildcard Policies. You can change your policy cards for free every time you unlock a Civic, or with Gold whenever you want.
Like with Technology, each individual Civic has their own unique in-game "side-quest" called Inspiration! moments, and like Eureka! moments some of these you'll get through playing the game regularly, and some will require some extra effort.
Faith: Like the above Culture and Science, Faith is accumulated per turn, and once a Civilization reaches a certain amount of faith, it gains access to a Pantheon which gives bonuses for their entire empire. Faith is used like an alternate currency like Gold and can be used to purchase religious units like an Apostle, Great People, special buildings and in Theocracy Government can purchase land combat Units. To achieve a Religious Victory your Religion must become the Predominant Religion for every Civilization in the game. A Religion is Predominant if it is followed by more than 50% of the cities in a civilization.
Districts: Each of the Cities now comprise Districts, (total of twelve district types, not including the city center) each with it's own different role and bonuses based on its type. Districts can unlocked through Technology and are limited by population, requiring 3 Citizens per district. Certain Buildings can only be built in some Districts, and at most can fit up to 3. Lastly, Districts gain bonuses based on what Terrain they are built on or surrounded by and can greatly boost your city output.