In TOAD, execute a query. Right click on the output Data Grid and select "Save As". In Format block select "XLS File". Adjust additional options (if necessary), specify "File Name" in "Save to" block and that should be all.
Without TOAD (or similar tool), spool the output as a comma separated values file (using, if possible, DBMS_OUTPUT package. If not, UTL_FILE). Open the CSV file using Excel.