The base of SEO is keyword. This line was used so badly during recent years that it leads to various bad practices like keyword stuffing, plagiarism and direct copy pasting etc. Google took some severe actions to correct the SEO habits and now again the content is king but still - Base of SEO is keyword. If you use ethically then there’s no bad in using the keyword within the content. To be on safe side keep the keyword density at adequate level. 3 to 5 percent keyword density is considered safe. 5 to 8 percent is still bearable and acceptable but going beyond that is putting your website at risk of getting banned by the next Google Update.
Apart from using keyword in content, it is very important if you have keyword in your URL as well. In the past, URL were not SEO friendly. There used to be different signs and symbols and codes in URL especially in the URLs generated by different CMS. Some CMS still not paying any attention on URL rewriting and that’s why users are running away from CMS. PhpBB is one of such CMS who still have coded URLs which are not SEO friendly. There are few more such CMS but in few you can get SEO friendly URLs by adding some plugin or addon.
About 7 years ago there published a blog post on most popular webmaster or SEO blog i.e. on MOZ. It was about “Anatomy of URL” and the author was Dr. Peter. Whatever he told in his cheat sheet is still valid and Google is also following that. In that cheat sheet you will know all about SEO friendly URL.
As stated above that SEO is all about Keyword. Having keyword in your domain or URL makes it easier for you to get ranked. If you are not lucky enough to get a domain having exact matched keyword in top level domain then you have the option to use keyword in URL to make it SEO friendly. An SEO friendly URL is a dynamic URL which doesn’t use symbols like &, >, #, $, %, ^, :, ; @ etc followed by some digits. Rather SEO friendly URL have words which speak itself that what’s inside that URL. Example of old style URL is www.abc.com/index.php?post=7846&sort=date&comment=5. While an SEO friendly URL looks like this: www.abc.com/history/when-stonehenge-was-built/
Now by looking at both links you can easily see that which looks better and easy to understand. In the first you don’t know what’s this URL is about but when you look at an SEO friendly URL, you can easily judge that this URL wil lead you to some post where Stonehenge history would be discussed. It gives users some ease and facility that’s why Google loves these dynamic SEO friendly URLs and ranks them high.
If you are using some CMS like WordPress or Joomla etc, you will get freely available plugins which can rewrite URLs in best SEO friendly style. Here you will have to do nothing much as everything will be done automatically. You just have to setup once and will have to customize the URL template and for the next time the plugin will do all itself.