Regarding installation of fedora 18
 

After i selected language and keyboard, it is asking 'what type of media contains the packages to be installed?', iam installing fedora through dvd..please help me here..

bad news
Fedora 18
Fedora 19
Fedora 20

are ALL end of life and not supported

please use a current and SUPPORTED operating System

Fedora 22

The answer to your question on f18 is to select the option "Auto-detected install media." The installer shows a picture of a cd/dvd device and since you are using a dvd, select that option.

If you are installing f18 to get some experience with fedora, or perhaps it's the only dvd you have, then it's good for having a look and feel for the distribution. It was quite a stable version of fedora. If you want to use that version on the internet, it could be problematical because security updates and package updates stopped for that version some time ago, so there is some risk of being attacked and some risk of packages crashing. However, I think you will find that most of it works quite well still. I wouldn't be including any data in it that I wouldn't be prepared to lose though.

BE WARNED!!!
fedora 18 is MISSING a OVER A YEARS WORTH of security updates
it went END OF LIFE on 2014-01-14
-- DO NOT USE --
you would NOT run Windows 7 or 8 without INSTALLING A FULL YEARS OF UPDATES AND SECURITY UPDATES!!!!!!
so do not do that with Linux

If you have a latest/recent hardware then installing in a VM like VirtualBox would be more sensible for Fedora 18.

If you are new to Linux then perhaps get a latest Fedora 22 DVD. It would save lots of pains, headache and frustrations.

Fedora 22 is a better option than f18 for regular and reliable use because it's currently supported, but there are in fact many older unsupported distributions running successfully. You can search for them on the internet and read many stories of fun, survival and patching. The world is a very varied place. To the OP, there's no need to be put off by the louder voices of self-appointed "installation police." You are surely free to make up your own mind. I know of a fedora core 2 system that is still working fine and accesses the net from time to time on dial-up.