What License you have to use if you just upload a game? It is important?
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Do you want to allow users use assets or code of your game? If not, you don't need to change anything...
License is about permissions of user. What user can/can't do with the work. https://en.wikipedia.org/wiki/License
Each license describes different permissions and "behaves" different.
website i recommend about choosing a license: https://choosealicense.com/