FileStreaming Principles

I recently worked on a project that includes a lot FileStreaming

that I still haven't touched on.
To get a better understanding of the principles of such methods, I wrote a code that (in theory) loads a file from one dir

to another, and went through it step by step, commenting in my understanding what each step achieves, like this ...

Get fileinfo object from DownloadRequest object

RemoteFileInfo fileInfo = svr.DownloadFile(request);

      

        
        
        
      

    

DownloadFile Method in WCF Service

public RemoteFileInfo DownloadFile(DownloadRequest request)
            {
                RemoteFileInfo result = new RemoteFileInfo(); // create empty fileinfo object
                try
                {
                    // set filepath
                    string filePath = System.IO.Path.Combine(request.FilePath , @"\" , request.FileName);
                    System.IO.FileInfo fileInfo = new System.IO.FileInfo(filePath); // get fileinfo from path

                    // check if exists
                    if (!fileInfo.Exists)
                        throw new System.IO.FileNotFoundException("File not found",
                                                                  request.FileName);

                    // open stream
                    System.IO.FileStream stream = new System.IO.FileStream(filePath,
                              System.IO.FileMode.Open, System.IO.FileAccess.Read);

                    // return result 
                    result.FileName = request.FileName;
                    result.Length = fileInfo.Length;
                    result.FileByteStream = stream;
                }
                catch (Exception ex)
                {
                    // do something
                }
                return result;
            }

      

        
        
        
      

    

Use returned FileStream from fileinfo to read into new write stream

// set new location for downloaded file
string basePath = System.IO.Path.Combine(@"C:\SST Software\DSC\Compilations\" , compName, @"\");
string serverFileName = System.IO.Path.Combine(basePath, file);
double totalBytesRead = 0.0;

if (!Directory.Exists(basePath))
    Directory.CreateDirectory(basePath);

int chunkSize = 2048;
byte[] buffer = new byte[chunkSize];

// create new write file stream 
using (System.IO.FileStream writeStream = new System.IO.FileStream(serverFileName, FileMode.OpenOrCreate, FileAccess.ReadWrite))
{
     do
     {
        // read bytes from fileinfo stream
        int bytesRead = fileInfo.FileByteStream.Read(buffer, 0, chunkSize);

        totalBytesRead += (double)bytesRead;

        if (bytesRead == 0) break;

        // write bytes to output stream
        writeStream.Write(buffer, 0, bytesRead);
     } while (true);

  // report end
  Console.WriteLine(fileInfo.FileName + " has been written to " + basePath + "  -  Done!");

  writeStream.Close();
}

      

        
        
        
      

    

What I was hoping for was any clarification or expansion of what exactly happens in use FileStream

.
I can achieve loading, and now I know what code I need to write to perform such loading, but I would like to know more about why it works. I cannot find "beginner-friendly" or step-by-step explanations on the internet.

What's going on behind the scenes here?