I am little confused about external linking. Is this good or not? If yes then please let me know that why we should do that?
Yes external linking is helpful. When search engine search a site then it's follow up that. It's good for us.
External links helps ranking good in search result. This is the important technique of SEO. So, external links are helpful for ranking good in search result.
You should get as many quality links TO your site as you possibly can. There are some quality tools out there paid and free. I've been using social monkee recently which is free and have had some good results - you can google that or click my signature
Yes, backlinks are most important factor in SEO...So alway try to get quality backlinks for your website