This library makes use of https://fortnitetracker.com/site-api.
Make sure to request an API key there and follow their guidelines.
Click here for the NuGet page.
Run Install-Package FortniteApi in Tools > NuGet Package Manager > Package Manager Console.
Right click your project in Visual Studio, click Manage NuGet Packages.., make sure Browse is pressed. Search for FortniteApi and press Install.