What does drop table SQL injection do?

  The vast majority of web applications do not allow query stacking. The Drop table SQL injection application can allow for query stacking if you use the mysqli::multi_query()or mysqli_multi_query() functions.

You can exploit these systems using sub-select, union-selects, blind sql injection, into outfile, or loadfile(). SQLMap and Havij are both tools that automate the exploitation of SQL Injection. SQLMap is a great tool with a wide range of features, and supports a wide verity of injections and DBMS'es.