Thanks Peter for your reply.
I think I get the first part that on reset the core will boot from 0x00.
However for the second part I am still not sure how is the ROM involved? Is there an actual separate ROM or the word ROM is used interchangeably with the flash?
In the reference manual it says "When Chip startup from BOOT ROM then jump to flash", so it seems there are two different entities, however there is no information stated about that ROM in the reference manual, that's why I am confused.