Concept of SEO
Relevancy: an important factor for Search Engine Optimization
First, let's talk about relevancy. When a user searches for something like "wordpress themes", search engines want to show you a list of results that are relevant to the topic of wordpress themes. Search engines will analyze all of the web pages that they have ever visited and pick out the pages that they believe are the most relevant to wordpress themes. They determine this by evaluating a lots of different factors including how your content is written and implemented in code as well as how other websites around the internet are linking to you and all of this stuff into a very big, very complex and very per priority algorithm. At the end of the day and in a fraction of a second a search engine is then able to rank and display all of those web pages in order of relevance to that phrase that the user just typed in, "wordpress themes".
This is very important to understand, because the search engines make a very clear distinction between content that's about wordpress themes versus content relevant for other phrases like wordpress plugins. Search engines are able to understand quiet a bit about semantic and thematic results between words and concepts. Take another example, "dog crates". A search engine knows the pages selling dog crates are extremely relevant to that search query. But it also knows that websites about pet carriers are also very relevant. It also knows that a website promoting things like pet food and dog toys might also be relevant to that search query but perhaps less so.
You may Also Like: Why Your site is not being indexed
Authority: Another important factor in Search Engine Optimization
The other fact that influences search engine exposure is authority. In other words out there in the large worldwide web, where anyone can post anything. Is your website a trusted place on the internet that the search engines would want to to show to their users? One very common way that the search engines determine the authority of a web page or a domain is by evaluating what other websites think of you, and this can be measured through the links out there that are pointing to your website. You can think of a link as a vote on the internet. A web page linking to your website is almost like saying "hey I trust your content enough that I'm willing to reference your page and possibly even send traffic to your site". It's a vote of trust and the search engines pick up on this as they crawl the web reading, evaluating and storing all the data that they can find on all the pages of the internet. But it's important to know right from the start that this is not just a popularity contest where you try to keep accumulate the votes on the internet.
Search engines have safe guards in place to prevent this kind of abuse and instead place an emphases quality of a link. For example, a search engine is more likely to trust a link if it comes from a well respected or industry related site like an industry leading blog or a non profit or a government agency that's involved in your field of work. A link coming from a one month old site that has nothing to do with you or your industry right above some text that says "all linked to anything you want for $5" is not going to be valued nearly as much. From the search engines perspective some links are more effective than others in casting their vote to your website and determining your site's authority. So you might think of this whole system as a waited democracy, where some votes are worth more than others.
You May Also Like: Using Google Plus Pages for Better SEO