Your question is unclear to me.
If you have an array of StringBuilder, then do this:
StringBuilder[] sb = new StringBuilder[] { new StringBuilder("A"), new StringBuilder("B") };
foreach (StringBuilder s in sb)
{
MessageBox.Show(s.ToString());
}
If that is not the case. Then do this:
StringBuilder sb = new StringBuilder("Tarun");
for (int i = 0; i < sb.Length; i++)
{
MessageBox.Show(sb[i].ToString());
}