For reading and writing data you use different byte stream as well as character stream . Mostly developer recommand character stream ,
First of all include namespace
using System.IO;
Reading:
FileStream fs = new FileStream("FileName.txt" , FileMode.Open);
StreamReader sr = new StreamReader(fs);
string s;
while((s=sr.ReadLine()) != null)
{
Console.ReadLine(s);
}
sr.Close();
fs.Close();
......................
Writing
FileStream f = new FileStream("FileName.txt" , FileMode.Create);
StreamWriter sw = new StreamWriter(f);
sw.WriteLine("String"); // You can write lines as you can
s.Close();
f.Close();