Do you mean “searchable” (as in a “site search” on your own site) or do you mean “indexed” (by search engines)?
If you are referring to Google searches you are talking about Google INDEXING your site. Google used to use the KEYWORD meta tags to help but it’s my understanding that the use of keywords in the meta-tag is now an old practice and KEYWORDS meta info is not used much. Google has their own methodology for indexing your page and ranking it. To learn about all this just search the web for “Google Ranking” and similar terms.
If you are talking about site searches (using a search box to find things on your site) then you need a tool to do that. There are some RW add-ons that allow site search, there are also tools “outside” of RW that you can use. I use a great search tool name Zoom search. But it is probably above the needs and capability of the average user (it’s a stand alone php script that you install and configure on your server.)