performance tuning in abap faqs

1. What is performance tuning?
   
2. What are steps you follow to improve the performance of
   a report ?
   
3. what is the role of secondary index in performance?
   
4. what is the role of ST05 in performance tuning?
   
5. what is the role of extended syntax check in
   performance tuning?
   
6. will join conditions in sql queries affect perfomance? how?
   
   
7. will sorted internal tables help in performance?
   
8. will where conditions in a sql query help improve
   performance?
   
9. does select single *.. / select * .. affect performance ?
   how?