Note that before installing the NuGet packages, you need to create a .NET 6, 7 or 8 project of the desired type. The NuGet packages get installed "into" the project.
Use this procedure also when your development environment is Visual Studio Code.
In order to install a OPC Data Client NuGet package and reference it from your project:
Open a command prompt.
Navigate to the directory of your project.
Type the following: dotnet add package OpcLabs.QuickOpc. This command adds OPC Data Client package reference to the project file.
If you need to add more packages (see List of Component Packages), repeat the dotnet add package command, giving it the package Id as an argument.