In the early days of web design, the idea was that tags could be used to help search engines to produce relevant results. However the fight to get particular websites near to the top of the ratings of Google (et al) meant that some website designers would happily add tens of thousands of tags to their websites, making the whole system rather meaningless. So nowadays search engines largely (or totally) ignore tags.
Keywords can be more useful but you'll still find plenty of websites where the bottom part of the page is taken up by hundreds, or even thousands, of keywords. (They'll be in very small script or even in white type on a white background, so that Google's web crawlers can see the text but the page visitor can't). So, while keywords can help search engines up to a point, they can still end up being less useful than the site designer might have planned on (simply because there are thousands of other websites using the same keywords).
What search engines really look for these days are websites which have got loads of links to them on other sites, suggesting that they might be genuinely of interest to people. However that results in the sort of spam that we get here on AB in the early hours of each morning, where there are loads of posts containing links. The spammers couldn't care less that nobody here is likely to click on those links. They also couldn't care less that a moderator is likely to to zap those posts within a few minutes. They know that Google's web crawlers check this site continuously, so those links will have been picked up, boosting the relevant sites' rankings.
So what you really ought to be trying to do is to work out how to get plenty of links to your website(s).