What is a keyword?
A keyword is a word that describes your product, service or web page you are trying to market. For example this article could have the keywords: "Keywords", "Affiliate", Internet", "Products" etc. The main use for these keywords is describe what is found in the product or on the web page.
The internet is driven by keywords, search engines are the traditional use. When you search for a specific keyword in a search engine you will get results based upon that keyword, modern search engines look for keywords in the domain name, web page title and throughout the content. In a blog a keyword is known as a tag and is used by the search engines in exactly the same way as a keyword.
Why one keyword is not enough?
If you tried to search for "internet" in Google you get around 2 billions results, wow, that's a lot. If however you searched for "Internet Marketing" you get 86 million results, yes I know this is this a lot. Lets take it a step further if you search for "Internet Marketing Advice" you get around 1 million results.
The more keywords you search for the more specific the search and the fewer results you will get. We could then categorize this article under "Affiliate Marketing", "Internet Marketing Secrets", "Selling Affiliate Products".
The Most important word "Relevance"
All your keywords must be ultra relevant to the contents of your subject. For example in the case of this article all the keywords need to be based around keywords and affiliate products as this is the content of this article. The words in the title are picked up as keywords so the article content must use the same words.
How do you research keywords?
One of the best tools to use is Google's free keyword tool. You can find it by searching for "Google AdWords Keyword Tool". You can then type in a keyword and Google will generate you a list of similar relevant keywords. Each keyword includes data showing you how popular that word is and how much competition you have with that word. This tool will generate you a whole host of keywords and keywords phrases you may have never thought of.
What can I do with my keywords?
Once you have generated your list of keywords you can use them to help you sell your affiliate products.
Articles: When you write a article make sure that your main keyword is in the article title. That keyword must appear throughout the body of the article but it must not be used excessively about 4 times is good, if you use keywords too much your article will look like spam and be rejected by the search engines.
Websites and Blogs: Your main keyword needs to be in your web page title as this is the first thing search engines look at. The keyword must then appear in the web page content, again up to 3 or 4 times. You should also have your keyword present in your heading or h1 tag. If possible including your keyword or part of your keyword in your domain name. When a search engine looks at your web page if it sees your keyword in all these places it will know that is what your web page is about.
A word of caution
It is all too tempting to try and optimize a web page for multiple even tens of keywords but don't. For each web page, blog post or article you should try and focus on on more than 3 keywords or keyword phrases. If you use 3 keywords they must all fit into the same niche for example "Affiliate Business", "Affiliate Web Marketing", "Affiliate Products".
I wish you the best of success.