is there any sites that we can use free content for our websites? what are those sites? can we use wikipedia.org content for our websites? anything else?

Why are you putting up a website if you don't have content / a plan for it?
And what would bring visitors to your site if it's just a copy and paste of other content?
But to answer your question, there are sites that offer content for usage. I don't have any links but a search on Google should give you some.
http://www.google.com/search?q=free+content+for+websites&sourceid=navclient-ff&ie=UTF-8&rls=GGGL,GGGL:2006-18,GGGL:en

Why are you putting up a website if you don't have content / a plan for it?
And what would bring visitors to your site if it's just a copy and paste of other content?
But to answer your question, there are sites that offer content for usage. I don't have any links but a search on Google should give you some.
http://www.google.com/search?q=free+content+for+websites&sourceid=navclient-ff&ie=UTF-8&rls=GGGL,GGGL:2006-18,GGGL:en
He is totally right. If you're serious about your website you shouldn't be looking for free content to copy and paste. That won't get you very far, and you won't rank very high in search engine rankings.
You should write your own content, or perhaps hire someone to do it for you.
Hope that helps

Just think, why would you choose the lower ranked version in Google to the actual, original version?
It's bad idea.

free content is useful.if i want to define something,it is something difficult to define myself,if i take definition from wikipedia,there are good definitions are there,work will be easy for me.if i am going to present gk that if i have gk site,gk is same every where so i can use gk wherever it required.

you can use rss feeds to get content from other sites that offer it

You can use Wikipedia content freely (no cost), but you must comply with the terms of the GFDL license they grant you use of the information under. Images can be under many different licenses.
See http://en.wikipedia.org/wiki/Wikipedia:Reusing_Wikipedia_content for how to re-use Wikipedia content.

you can use rss feeds to get content from other sites that offer it
That's called scraping, and will get your site a complaint to your provider, if not a DMCA takedown notice.

using wiki is the worst thing to do ever. people put whatever they want on that. I could say the christian religion is about fish and people would use it for a report

You will need permission to copy and paste content as all published media is essentially copyrighted with or without the copyright notice. Many author's will glady grant permission, if you give them due credit. Content that has been copied and pasted can be tracked. Best to post content through your own research, or credit authors for theirs.

using wiki is the worst thing to do ever. people put whatever they want on that. I could say the christian religion is about fish and people would use it for a report
Not that this is the place for this debate, but: Yes, you could say the Christan religion is about fish. That's the power that "anyone can edit" means. However, it would be considered vandalism and it would be removed quickly (especially on such a high profile article) and you would possibly get a warning (many warnings = block from editing for awhile). So yes, while there are many vandals out there, most edits are positive, even if small (correcting punctuation or grammar). And in the whole, for major articles studies (yes, profession studies and reports!) have shown that Wikipedia is about as actuate as "traditional" encyclopedias in accuracy, breath and content. Just take it with a grain of salt like most anything on the internet and if you read it before you copy/paste (and follow the GFDL) on your website (or report, or...), you'll be fine.

You can use the content as ref which is better as unique contents tend to rank higher in SE. Using cut and paste will obviously be a turnunder for your site.