It will display as perform find [ restore] if you specify the find requests as part of the find.
Personally I do not use it most of the time because I like seeing my scripts manually set the fields when I debug as well as being able to set fields dynamically.
Enter Find Mode 
Set Field [ FName; "John" ]
Perform Find 
Would be the same as Perform Find [ Restore ], but where you have specified already that FName value be "John".
Does this clear things up?
Thanks mr_vodka. It was a good example dat u'd mentioned there. It surely clears things up.
When I use Set Field [ FName; $ID], if $ID contains "1", the find set will include "1", "11", "12" etc. how to specify the complete match option?
First, I dont know why you would be searching for an ID in a text field.
Second, to find exact matches you will to use "==" as a prefix. "==" & $ID.
Thanks for your answer, I am unlikely to find out the syntax by myself.
Anyway I've changed the text field into a number field and the problem is gone. But sooner or later the syntax is useful, thank you very much!
When I was doing my programming some twenty years ago, we are very cautious about the use of numbers, as the compiler are free to promote the type into a larger format without notice and that may break the code. So it becomes the second nature that I choose text as the index field type.