You can turn ordinary keys into a bump key simply by fashioning the edges of any key into sharp serrated points, which effectively enable the driver pin of any lock to give way to the turning of the cylinder of the key. A hook pick, which is sometimes called a ‘feeler’, is generally used to lift the pins individually, rather than ‘rake’ the pins simultaneously, so as to facilitate the unlocking mechanism, whereas a bump key turns the cylinder by aping the actual key mechanism. These lock picking tools such as bump keys can be used by people to gain entry into their homes in cases they have lost their original key, which they might get changed in the immediate future, but for temporary entry, bump keys make for the most effective unlocking system and can be used even by an amateur.
The insertion of such sharp serrations into a lock effectively disables the normal functioning of the pins, which in turn affects the elastic mechanism of the lock. Any simple lock does not necessarily need a proper key for the unlocking mechanism of the same to take effect. A bump key is used by professional locksmiths to pick locks that need to be opened without forcing the unlocking mechanism which might damage the lock to such an extent that the lock cannot be operated on in the future.
One word of caution: do not make a bump key if you have criminal intent! Of course, making them is easy, but using them illegally can land you up in a jail, so if you want to use them for recreational purposes, make sure that you try them out on the locks of your own home!