in wcf service operation contract use the follwoing connection string which is for sql azure code
SqlConnection con = new SqlConnection("Server=tcp:your server name;Database=Registration;user id=user id;password=password;Trusted_Connection=False;Encrypt=True;");
now write the code for inserting the data into the database by using following code
SQlCommand cmd=new SqlCommand();
cmd.Connection = con;
cmd.CommandText = "insert into DownloadsData values('" + pc.Username + "','" + pc.Title + "')";
con.Open();
cmd.ExecuteNonQuery();
con.Close();