It’s just pre compile SQL while run time it’s execute query.

prepared statement work same as the statement,but there r
some differences.

wen u submitting the query first time following things happened
1)compiling the query
2)executing the query
3)sending results back to the program

2nd time onwards
1)executing the query directly
2) sending results back to the program

Prepared statements are used due to its 2 advantages.

Advantages:
1) We can give dynamic values.
2) The statement will be compiled only once, it need not be 
compiled each & every time we give new values.

when we sent a sql stmt in to oracle sever the server 
splits statemts in to mutiple stmts, checks wheather valid 
or not, if it is valid it is stored in the shared pool,
 where as in the normal stmt parsing will be done every time
in prepared parsing will be done only once, naxt time 
onwards values will be sent to the place holders