i have an apple iphone 4 can i put siri on it ,if i can how?

Sorry, no.

There are a number of apps in the app store that provide some of the functions of Siri, but not all. You can do a search & see if anything meets your needs. That's as good as its gonna get for an iPhone 4. Your only other choice, if you want Siri, is to upgrade your phone to a 4S or 5.

Try Google app - use the Voice search. It's not going to text your friends or set reminders, but for quick searches it is probably the most incredible tool out there I've seen so far. And it's fast.