You can put your keywords in your website page main content and also you can use your important keyword in meta title or H1 tags and also in meta description but most important place is content of the website page.
You can add keywords in your meta keyword tags and cntent of your webpages, however your titles of webpages and content, description tags, alt tags also contain important and main keywords.
Keywords are those words which define what your website is all about. Those words have to appear in the content of the website, description, meta tags etc.