System.IO.StreamWriter

You use a StreamWriter object to write data to a text file.
There are a number of ways you can obtain the StreamWriter object

System.IO.StreamWriter oStreamWriter; 
oStreamWriter = new System.IO.StreamWriter("C:\Temp\textfile.txt"); 

Using a FileStream

System.IO.StreamWriter oStreamWriter; 
System.IO.FileStream oFileStream; 
oFileStream = new System.IO.FileStream("C:\Temp\textfile.txt", FileMode.Open); 
oStreamWriter = new System.IO.StreamWriter(objFileStream); 

Using a Stream
This lets you specify the mode, access and share

System.IO.StreamWriter oStreamWriter; 
System.IO.Stream oStream; 
oStream = System.IO.File.Open("C:\Temp\textfile.txt", FileMode.Create, FileAccess.ReadWrite, FileShare.None); 
oStreamWriter = new StreamWriter(objStream); 

Using File.OpenWrite

System.IO.StreamWriter oStreamWriter; 
System.IO.FileStream oFileStream; 
oFileStream = System.IO.File.OpenWrite("C:\Temp\textfile.txt"); 
oStreamWriter = new System.IO.StreamWriter(objFileStream); 

Creating a Text File

File.CreateText

System.IO.StreamWriter oStreamWriter; 
oStreamWriter = System.IO.File.CreateText("C:\myfile.txt"); 
oStreamWriter.Write("this is some text"); 
oStreamWrite.Close; 

Writing the Contents

There are several ways to write to a StreamWriter

Write a Single Line
This only works with strings and appends a newline character to the end.

string sText; 
oStreamWriter.WriteLine(sText);