How to create 3 tier

[WebMethod]
        public static List<string> GetAutoCompleteData(string Email)
        {
            List<string> result = new List<string>();
            try
            {
                var cmd = new SqlCommand("SesslogProc");
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.Add("@EmailId", SqlDbType.VarChar, 50).Value = Email;
                //Data.ExecuteSqlCommand(cmd);
                SqlDataReader dr = Data.ExecuteReader(cmd);
                while (dr.Read())
                {
                    result.Add(dr["EmailId"].ToString());
                }

                dr.Close();

                return result;
            }
            catch (Exception ex)
            {
                throw ex;
            }

        }