The best place to place keywords in a website is in the title of the page, in the first sentence, and in the last sentence. You can also use them throughout the body of the text, but make sure they are used naturally and not forced. Another thing to keep in mind is that you should only use a limited number of keywords on each page. Too many and it will look like you're trying to spam the search engines, which can get your website penalized. So choose wisely and focus on those that are most relevant to your topic.