While it’s been long since Google considered tge keywords tag, some so called SEO experts still insist on giving out bad advice, usually claiming that it’s important to include keywords for pages.
The keywords meta tag has been used in the past, but is now largely being ignored, because webmasters has been abusing it for spam, and to manipulate their rankings, or even make their pages rank for completely irrelevant keywords.
Therefor search engines had to move away from using the keywords meta tag, and in 2015, it is practically useless. You might still find the weird and rare site which uses it for something, but other than that, you shouldn't worry about it.
Page content important to modern search engines
The fact that the keywords meta tag is now useless, does not mean that keywords themselves are useless. Typically, search engines can instead look at the content of the pages they are ranking, and try to analyze it as part of the ranking process.
It’s therefor still important that keywords are located throughout the content of the page, and not just single words, but also the longer keyphrases. You shouldn’t create lists of words, or other unnatural methods to include keywords – write them as a natural part of your text.
Keyphrases are combinations of words in an article that are relevant to the article as a whole, and as such likely to make the article or page show up in the SERPs for certain search queries.
Typically the title of a page would be keyword-dense, but still natural to read, and relevant to the article itself. Throughout the content, relevant repetitions of words and phrases may affect the ranking of the page. As well as the natural use of certain HTML elements.
Off-site, other ranking factors can play in, such as the number of links pointing to a page, and existing competition within a topic or industry. These factors generally do not matter, what’s important is that you focus on delivering good content for your own audience.