create cname
 

I have a linux machine in amazon cloud I want to create a cname for this, please tell me how.

If you're adding this so you can reach your machine from the internet (WAN) then you need to use the domain control panel to accomplish this so you go to whomever hosts the domain then add a cname record so...
To do this you need to own exampledomain.com and go to the company that you registered this domain with (godaddy, hostmysite, whatever) and proceed to add the CNAME record from there. I'm sure their customer service or forums would be able to better help you with this.