how does C# know what Path class is without giving me have a line 'using System.IO'?

I have this snippet of code. Why does C# know what Path class is without giving me an error given that Path is in the System.IO, logically, I should include it. However, Visual Studio 2022 did not yell at that. And another question is does using Some.Namespace automatically import other files in the file structure in C#? Like in PHP, when we want to use some classes from another file, we have to import that file use require_once or in Python, we use the import statement.

using System.Text.Json;

namespace ContosoCrafts.Website.Services
{
    public class JsonFileProductService
    {

        public JsonFileProductService(IWebHostEnvironment webHostEnvironment)
        {
            WebHostEnvironment = webHostEnvironment;
        }

        public IWebHostEnvironment WebHostEnvironment { get; }

        private string JsonFileName
        {
            get { return Path.Combine(WebHostEnvironment.WebRootPath, "data", "products.json"); }
        }
    }

}