First up the disclaimer. There is a whole big thing called SEO (Search Engine Optimization) that is now so specialised you can hire experts to aid you in getting it right. What I'm offering here is very much an amateur's perspective, so keep that in mind. I imagine that anyone that knows better will correct me, but my understanding (and very limited experience) goes something like this:
The importance of keywords (as distinct from content) in site metadata has changed over time, largely because of abuse of the feature. This makes the topic more complicated than it need be. For most purposes (appearing on Google etc.) the content of your site will be indexed. So presuming you have a page or article or two that actually mention your book and some relevant details then your site will get indexed and available for searching.
Where hidden keywords may become more important is where you have a good book title like "The Things Kids Do". If your book is about children then you might want "children" in your site keywords, if it's actually about goats then "goat" and "goats" might need to be there. (Although if you have these words in the main text of the article then it may not matter very much.)
Access to site metadata depends on the software you are using. The theme I use under WordPress has a section dedicated to SEO that I have largely ignored at the moment. If you don't have access to assign keywords yourself then, as I suggested above, you may offset this lack simply by making sure your content contains the words you need.
And don't get too panicky about keywords - as long as the words you need are being found somewhere on your site. SEO is a much bigger topic than keywords. For example a major factor in your placement in search results involves how many sites link to your pages.
And to conclude with another disclaimer (because I hate sounding more knowledgeable than my credentials warrant): If in doubt, research. Read about SEO. Do some searches and see what comes up, check out the source for the top pages and see what they did.