What is the difference between the pornstar and the prostitution?

not much difference

Porno star shows you her body while you pay and play with yourself, and a prostitute has sex with you.

Few if any porn performers were prostitutes. Some places require background checks to prevent this. Performers in porn are actors and actresses. They  perform sex just like John Wayne murdered bad guys while playing a vigilante. You never called him a killer, did you?

Porn is acting. Sex or simulated sex might not even happen. Stand ins are often used for close-ups. Porn is entertainment. Prostitution is a service. Sex for money.

If you perform prostitution on video that magically makes it not illegal.

A pornstar "does" a few people per movie, and often has some choice in whom and what.

A prostitute "does" several people per day, and often cannot afford to refuse many customers/acts

Of course they both satisfy the same need, however the pornstar environment incudes sterile settings with similar acting partners filmed for the customer whereas prostitutes work their trade directly with the customer.  In the hierarchy of sex workers, pornstars are above prostitutes.  

I see no difference... They only f u c k e d for money