DataTable dt = new DataTable("MyTable");

DataColumn dc1 = new DataColumn("Field1", typeof(String));
DataColumn dc2 = new DataColumn("Field2", typeof(int));

dt.Columns.AddRange(new DataColumn[] { dc1, dc2 });

dt.Rows.Add();
dt.Rows[0]["Field1"] = "abc";
dt.Rows[0]["Field2"] = 1;