The dotnet nuget push command pushes a package to the server and publishes it. The push command uses server and credential details found in the system's NuGet config file or chain of config files. For more information on config files, see Configuring NuGet Behavior. NuGet's default configuration is obtained by loading %AppData%\NuGet\NuGet.config (Windows) or $HOME/.local/share (Linux/macOS), then loading any nuget.config or .nuget\nuget.config starting from the root of drive and ending in the current directory.
The command pushes an existing package. It doesn't create a package. To create a package, use dotnet pack.
(see also: Microsoft Documentation)