Where i find Siri on my iphone?

I can't get where is it? I checked app store, typed in search siri but didn't find it?

It depends on what iPhone you have. IPhone 4's can't get Siri. If your iPhone has it then you can just hold down the middle/home button and a small box with the words "what can I help you with?" Will appear. If it doesn't show up then you don't have Siri.

You can't download it.

You have to have the iphone 4s or 5 to have siri, the 3, 3gs and 4 don't have it. If you have a 4s just press and hold the home button stated above.