Where are the demos in the playstation store?

May be...

I am new to playstation 3 so i dont know can you help me?

When you log into the Playstation store, there is a menu on the right side. It has a section for demos. Click on that and it will take you to the demo menu.

in the xmb highlight Playstation Store and once you get in the menu go it will be there it will say demos and that is about it but you have to have a Playstation account in order to access the store

if you click on ps3 games then you can go into a category most of the games have demos.