A keywords data field is an integral part of each web page.
Search Engine Optimization (SEO) Tools may warn you, if you do not provide at least one keyword that is related to the content in a web page.
You do not need to write anything, if you do not really care if a particular page is to be part of search engine results. The real problem that you will have with keywords is that there may be more people out there using the same keywords than will fit on "page 1" of search engine results.
See also Domain Name Extensions
If you are a shop that is selling a component that you describe in a web page, you would probably write the name of that component into the the keyword list that belong to the said page.
However, now a days that would probably not be enough to get your component close to "page 1" in search engine results, because there could be several shops that have the same item on offer.
Integrating the name of the component type in one of the <h> titles as well as where your shop is to be found and placing the component name in your keyword list may place your product higher up in search engine results.
Here is a solution: Get a small group of persons to write down the words that they would use when searching for your product or information.
If any of those keyword get you closer to "page 1" in any of the web browsers you may want to think about keeping it in your keyword list.
Even for so called text writers and so called bloggers, good keywords selection can help. If your writing allow it, try targeting a different place in different intervals, by having a place in your text for the names of places and changing those names in regular intervals.
Keywords can be more than one word in length.
Are your keywords and or phrases things that surfers would write when they are looking for something?
SEO Tips and Tricks - Selecting keywords that help search engines point users to your internet content