can you please elaborate

Sure...
Note that I am very much self-taught so may use incorrect terms and make assumptions - others will hopefully correct any errors I make.

A Temporary Table is much like a regular table in the RDBMS except that it created on the fly by your code. It is automatically dropped by the RDBMS when the database session ends. So it only exists within the current running instance of your code.

So a common use for a Temporary Table is to gather together data from various different sources (usually other tables) so that SQL operations can be performed on all the data at once. For example, in my CRM I have a reminder view. This takes birthdays from the 'Person' table, reminders from the 'Note' table, anniversaries from the 'Anniversary' table, etc. It loads all this into a Temporary Table before sorting in into date order and showing just the first 20 events.

This code snippet is ancient legacy code and I wouldn't write it quite like this now but it should give you the idea of pulling data from different places and then working on the combined result.

In this example, all the data sources are within the same database schema. But they could be in different schemas within the same RDBMS or different RDBMS's. They could be on different machines in different locations potentially accessed over ODBC. They don't even have to be data sources from databases - they could come from anywhere.