stream reader/stream writer if you want it to be a text file or binary read/writer for binary files (.dat or w/e)
Example code...
Code:
StreamReader SR = new StreamReader(File.Open("filename.txt", FileMode.Open));
string AllFile = SR.ReadToEnd();
string[] FileLines = AllFile.Split('\n');
foreach (string S in FileLines)
Console.WriteLine(S);
SR.Close();
Here's an example of a writer
Code:
StreamWriter SW = new StreamWriter(File.Open("filename.txt", FileMode.OpenOrCreate));
SW.WriteLine("Line 1");
SW.WriteLine("Line 2");
SW.WriteLine("Line 3");
SW.Flush();
SW.Close();
VERY basic applications of both systems but hopefully it gives you some ideas.