What are keywords? Keywords, in their most basic definition, are specific words that are used in text and headlines to reflect what a website is about. For example, if you've got a website for your real estate business, using the words like "real estate", "realty" and "realtor" are important to your website's success. Essentially, using the right keywords is just as important to the success of your website(s) and business as many other elements. Look at it this way: if you listed your business in the yellow pages, what would it be categorized under? This will be the main keyword you want to use, and then you can develop secondary ones based on the main category.
Writing your website headlines and content around a set of keywords that you integrate is known as Search Engine Marketing or Search Engine Optimization (SEM and SEO, terms you've probably seen before). What you do is to research your particular type of website and see what other people use to get the best rankings on a search engine. For example, if you've got a website for music memorabilia, you would search this on Google or Yahoo, and see which pages come up first. Then you can borrow keywords and popular phrases from these sites (it's not plagiarism if you only borrow 2-3 words, it's keyword use!!) to increase your site's ranking so that more people will see it.
Effective SEO writing (keyword based writing to increase your rankings on search engines) generally allows for a 5-10% keyword density in your articles. In a 100 word article, that's about 5-10 uses of your keyword. Any more, and Google will kick you out of the rankings for what is known as "keyword stuffing". Basically, they are preventing people from getting traffic to their websites without legitimate content. By using keywords properly and in their most basic form, you can help increase your search engine rankings and the traffic to your website.
The goal of effective keyword use is to get your website(s) listed on the first page of the search return. Otherwise, it'll probably never get seen. How many people do you know that actually check past the first page of results for answers to their search? To sum up, here is a quick review:
If you're in better understanding of this topic, but still not 100% certain of what's involved in marketing your website through the use of keywords, you can hire a writer that specializes in SEO/SEM writing and keyword use. There are hundreds of job boards out there to find them, and thousands of writers who'd love the work.