Back link

What is back link ?
Back link is the main key of SEO, if you want to do SEO, first will be need back link. Back link are two kinds:
1. Do Follow Back link.
2. No Follow Back link.
If you want to start SEO, you will need four kinds of back link:
1. Profile link building back link.
2. Social bookmarking back link.
3. Blog commenting back link.
4.Forum posting back link. 
I give here here some back link to do SEO.........
For profile link building............

http://moda.com.pe/foro/index.php?action=profile;u=698783;sa=summary http://forum.vup.hr/index.php?action=profile;u=16519;sa=summary http://forums.eyeos.org/index.php?action=profile;u=37467;sa=summary

For social bookmarking..........

bookmarkingpro.com/story.php?title=factual-details-about-imitinef-mercilet-%7C-what-where-n-how#discuss
bookmarkknight.com/story.php?title=factual-details-about-imitinef-mercilet-%7C-what-where-n-how#discuss
bookmarkinstant.com/story.php?title=factual-details-about-imitinef-mercilet-%7C-what-where-n-how#discuss