I'm preparing my resumé but I'm stuck on a point. I'll write a reference and as far as I see usually there is a references title in most resumés then details. But, I have just one reference. What should I write references or reference for the title?
For internships, you'll probably be asked for your references during the application process (either on a form online, or on a form on paper).
I can only speak about the US, not Turkey.
But in my opinion, a candidate should never plaster the contact information of his references on his resume for everyone to see. I've seen candidates do that, and usually I think to myself that such candidates are disrespectful to their references for having done that.
If you want, you can include that "references are available upon request", but in your case, I would just omit that part. That "references are available upon request" is a given for any resume.
And the fact that you only have one reference to give is a red flag. So do not call attention to that fact early in the process if you can help it. That being said, consider doing some volunteer work, or getting some personal references from older friends/mentors.
At your age, it's expected that you may not have any work experience yet, but you should still try to have a minimum of two references, even if they're not professional references. Also, know that references are only usually checked once they've decided to hire you, or once you've made it to the final round. Checking references too early in the process just takes too much time otherwise. That is why, it would be premature to list them in your resume.
That being said, as a sanity check, verify that what I am saying applies to Turkey as well. If out of three Turkish people, two of them tell you to include such a header, then do as they say, and forget what I said. Follow the most common conventions in your country.