temp-table

whats the purpose of temp table and work table?

Quoting the documentation again:

"A temp table is a set of fields (columns) that temporarily stores multiple rows of data during a session. It generally exists only for the duration of the procedure that defines it, or at most for the duration of a session. A field in a temp table can be a direct copy of a field in a persistent database table, or it can be derived from other fields or data sources."

Temp-Tables can also be used to transport data between clients and the app server. Temp-Tables can be serialized to XML and JSON.

And:

DEFINE WORK-TABLE statement

Defines a work table (a temp-table stored in memory) for use in one or more procedures, or within a single class.

This statement is supported only for backward compatibility. Use the DEFINE TEMP-TABLE statement, instead.

For more information, I recommend the product documentation / online help? Or do you have specific questions?