you get a backlink when you do various things like link building which includes directory submissions, article submissions, blogging etc.
You can get back links through: Link Building Article Submissions Blogging Directory Submissions Social Bookmarking RSS Submissions
Check out link development category http://forums.digitalpoint.com/forumdisplay.php?f=13 u will have more information about link building.
backlink is just a link of your site in another page or site. there are reciprocal link or one way link, "dofollow" link or "nofollow" link and internal link or external link.
Easy. Either ask someone to link back to one of the pages on your site, create another site and link both sites to each other, or write something authoratiative that people will want to link to. You can also put a link to your site in your forum signature (once you've met the minimum requirements here anyway) though the link won't be worth much to search engines. That too. Though I wouldn't worry about article submissions. You don't want multiple copies of the same content running around. It's kinda like having a Homer moment - multiple Homer Simpson "clones" being created by a spinning hammock. Which one's the real one? (Hint: if you picked Peter Griffin from "Family Guy" you need to see an optometrist.) Why buy something you can get for free (via your own signature space)? Forum signature link buying has always seemed like a stupid idea to me. Not really. If you have two relevant pages that appear to be naturally linking to each other then I'd say yeah. But if two pages are just linking to each other for the heck of it, then don't bother wasting your time. Yup, and "dofollow" is the default on most Web sites (unless they've been modified via META tags or a robots.txt file, or they're using WordPress, which adds rel="nofollow" to links posted in comments). Bingo!