string convert = "This is the string to be converted";

// From string to byte array
byte[] buffer = Encoding.UTF8.GetBytes(convert);

// From byte array to string
string s = Encoding.UTF8.GetString(buffer, 0, buffer.Length);

Assuming that you are using UTF-8 encoding:

string convert = "This is the string to be converted";

// From string to byte array
byte[] buffer = System.Text.Encoding.UTF8.GetBytes(convert);

// From byte array to string
string s = System.Text.Encoding.UTF8.GetString(buffer, 0, buffer.Length);

string convert = "This is the string to be converted";

// From string to byte array
byte[] buffer = Encoding.ASCII.GetBytes(convert);

// From byte array to string
string s = Encoding.UTF8.GetString(buffer, 0, buffer.Length);

string convert = "This is the string to be converted";

// From string to byte array
byte[] buffer = Encoding.UTF8.GetBytes(convert);

// From byte array to string
string s = Encoding.UTF8.GetString(buffer, 0, buffer.Length);