analyze table t validate structure cascade quesiton

 i just meet some situation, that like block corrupt  and table high water and sql tunning

1.block corrupt 

just from analyze table t validate structure cascade

2.table high water

SQL> analyze table test1 compute statistics;

Table analyzed

Querying dba_tables for 'Blocks' and 'Empty_blocks' should give the high water mark.

Blocks -- > Number blocks that has been formatted to recieve data
Empty_blocks ---> Among the allocated blocks, the blocks that were never used

3.sql tunning

exec DBMS_STATS.GATHER_TABLE_STATS(OWNNAME => 'imuse01', TABNAME => 'SUBSCRIBEINFO', GRANULARITY => 'DEFAULT' ,CASCADE => TRUE);

maybe i am freshman, so  i want to ask a quetion,  can  any explain