Backlink is a link one website gets from another website. Backlinks make a huge impact on a website’s prominence in search engine results. This is why they are considered very useful for improving a website’s SEO ranking. Search engines calculate rankings using multiple factors to display search results. No one knows for sure how much weight search engines give to backlinks when listing results, however what we do know for certain is that they are very important.
I’ve seen so many cases of webmasters nofollowing legitimate external links it is not funny. Any external link on their site is nofollowed, even when quoting text on the other site. IMO, the original purpose of nofollow has long been defeated in specific industries. As more webmasters continue doing everything they can to preserve their pagerank, the effectiveness of nofollow will continue to erode.
A backlink is a reference comparable to a citation. The quantity, quality, and relevance of backlinks for a web page are among the factors that search engines like Google evaluate in order to estimate how important the page is. PageRank calculates the score for each web page based on how all the web pages are connected among themselves, and is one of the variables that Google Search uses to determine how high a web page should go in search results. This weighting of backlinks is analogous to citation analysis of books, scholarly papers, and academic journals. A Topical PageRank has been researched and implemented as well, which gives more weight to backlinks coming from the page of a same topic as a target page. 
Black hat SEO is to be avoided. This is basically link spamming. You can pay somebody peanuts to do this on your behalf and, for a very short period, it brings results. Then Google sees what’s happened, and they delist your site permanently from search engine rankings. Now, you need a new website and new content, etc.—so, black hat SEO is a terrible idea.
The green ratings bars are a measure of the importance Google’s assessment of the importance of a web page, as determined by Google’s patented PageRank technology and other factors. These PageRank bars tell you at a glance whether other people on the web consider Google considers a page to be a high-quality site worth checking out. Google itself does not evaluate or endorse websites. Rather, we measure what others on the web feel is important enough to deserve a link. And because Google does not accept payment for placement within our results, the information you see when you conduct a search is based on totally objective criteria.
Changes to the algorithms that produce search engine rankings can place a heightened focus on relevance to a particular topic. While some backlinks might be from sources containing highly valuable metrics, they could also be unrelated to the consumer's query or interest. An example of this would be a link from a popular shoe blog (with valuable metrics) to a site selling vintage pencil sharpeners. While the link appears valuable, it provides little to the consumer in terms of relevance.
Less than 2 years ago one could promote a website within a month with the help of PBN (Private Blog Network). Then Google created “a sandbox” which made a site owner wait no less than 3 months before the effect of PBN backlinks turned to be visible. There are two more negative factors: risk and financial investment. You will realize that neither your wasted time nor money were worth it. That’s why it’s better to rely on proper backlinks from real sites.
Something a lot of people seem to have overlooked was hinted at in Greg Boser’s comment above. Greg identified that there is a major (and unfair) disparity with how authority sites such as Wikipedia disrupt the linkscape by run-of-site nofollows. Once Wikipedia implemented the no-follows, previously high-value links from Wikipedia were rendered worthless making the site less of a target for spammers. Increasingly large sites are following suit in order to cleanse their own pages of spam.
btw; All those SEO’s out there probably made some monies off clients, selling the sculpting thang to them. I know some are still insisting it worked, etc, but would they say in public that it didn’t work after they already took a site’s money to sculpt? How would anyone judge if it worked or not definitively? The funny thing is, the real issues of that site could have been fixed for the long term instead of applying a band aide. Of course; knowing the state of this industry right now, band aides are the in thing anyway.
Website owners recognized the value of a high ranking and visibility in search engine results, creating an opportunity for both white hat and black hat SEO practitioners. According to industry analyst Danny Sullivan, the phrase "search engine optimization" probably came into use in 1997. Sullivan credits Bruce Clay as one of the first people to popularize the term. On May 2, 2007, Jason Gambert attempted to trademark the term SEO by convincing the Trademark Office in Arizona that SEO is a "process" involving manipulation of keywords and not a "marketing service."
Try to publish periodically. Thanks to that you’ll keep your users. Naturally, it’s almost unreal to write masterpieces daily, but you must NOT forget about your users and please them with new information, if not daily then at least every week. Use an editorial calendar and try not to change it. Then you’ll produce new posts automatically. There will be no need for constant reminding.
9. Troubleshooting and adjustment. In your first few years as a search optimizer, you’ll almost certainly run into the same problems and challenges everyone else does; your rankings will plateau, you’ll find duplicate content on your site, and you’ll probably see significant ranking volatility. You’ll need to know how to diagnose and address these problems if you don’t want them to bring down the effectiveness of your campaign.