7-Step SEO Basics for Beginners: Link Building
The search engines will use back links to find further pages and decide from the overall quality how pages should rank compared to other pages in their indexes.
Linking to relevant and authoritative sites in itself doesn't raise your ranking but it does show you are more serious in your subject area than spraying links out to junk astro-turfing sites of no quality or relevance.
More importantly, the search engines rank higher when there are back links to you from external sites with authority and relevance. Links from other sites may not be under your control but will push you up the indexes if they are from authoritative sites in your subject area. It's like moving upmarket into a better neighbourhood.
Conversely, getting into link exchanges and link networks with no value-add will diminish your page ranking - it's about quality, not quantity.
It’s better to have a few links from good sites than lots of junk and irrelevant links just to look busy.
Link building is a bit part of the SEO business. Beware the commercial link builders, the search engines are onto them and their tricks, such as closed link-wheels that only reference the sites within a number of thin, link-bait sites.
Reputable link building tactics include guest blogging for reputable sites in your subject area, where you can write a guest post and link back to your own site.
If there are unlinked references to your site from other sites, get those to include an explicit link.
Use the same links as your nearest competitors as relevant references in your content. This has to be relevant and related and not just link-stuffing which risks devaluing your site and those you link to.
There are many more legitimate link-building tactics we can dive into another time. RC