This will teach you how to recurse through a directory/filesystem using C#..
The problem comes from not knowing how many folders/files exist.
One folder can have many folders inside it, those folders can each have many folders inside it.

I will show you how to recurse through the filesystem and explain it so that you UNDERSTAND it. This isnt for copy-paste.

We will start with a C# console application and pick a path, we'll use C: for this.
First of all, we're going to need the IO namespace. The IO namespace has access to File and Directory methods.

At the top add these lines:

using System; //Just so we can use the shortcut Console instead of System.Console
using System.IO; //Gives us access to file, directory objects

Now, in our "main" method, we are going to write the following:

string path="C:/"; //set the root path we want to recurse through.

//check if the directory exists
if(Directory.Exists(path)){
        DirectoryInfo di=new DirectoryInfo(path);
        //based on a path, this object will give you directory information about that directory
        printDirectories(di);
        //this method will actually go through our directories and print out information
}else{
        Console.WriteLine("Directory does not exist. Press Enter to exit");
        Console.ReadLine(); //when you hit return the program will terminate.
}

Now we will write the print directories method. It takes a DirectoryInfo object as a parameter and will use that to recurse through the file system.

//declared as static because were a console app, this can be private in your application if it a utility method.
2 Important methods we're going to be looking at are in the DirectoryInfo object. They are

public FileInfo[] directoryInfoObject.GetFiles() //returns an array of FileInfo objects
public DirectoryInfo[] directoryInfoObject.GetDirectories() //returns an array of DirectoryInfo objects

static void printDirectories(DirectoryInfo di){
       foreach(FileInfo fi in di.GetFiles()){
              //we are going to run code for each file
              Console.WriteLine(fi.FullName); //this prints out the full file name including the path
       }

      //now that we process this directory for files, we do the same for every subdirectory in this directory
      foreach(DirectoryInfo subDir in di.GetDirectories()){
             //we are going to call the printDirectories method, with the subdirectory as the root.
            //its files will be processed, then its subdirectories will be checked
            //this happens foreach Directory in the current directory
            printDirectories(subDir); //recurse
      }
}

Thats simple recursion. The most common use of this is for populating a treeview and another use that comes to mind is file searching. Keep an eye out for the next tutorial: Populating a Treeview from a file system!