Sort is an operation performed by oracle when u want to arrange data with respect to by name,or company.
Generally when u use group by,order by or any group function in ur sql statement oracle will perform sort operation on the column used in the group by or order by clause.

SORT_AREA_SIZE is the parameter set to allocate this amount of memory for oracle to perform sort in the memory.
If the sort operation requires more space than this,the oracle will allocate temporary segment in the temporary tables and perform sort operation their.

SORT_AREA_RETAINED_SIZE is the amount of sort area retained after oracle performs sort operation.

temporary tablespace is used by all the users in the database.

regards
anandkl