google bot access my site. so something happen. index my page and cache my page. does it mean the same thing?
yes, both are same. To know how many pages of ur site is indexed you can do search in google - site:yourdomain.com
Index your page means that "Yes, we've added your site to our search results". Cache your page means "This is the snapshot we have about your page" - useful to get an idea of how often they crawl your site. Ie., if the Google Cache is a snapshot of your site from 2 months ago, then you know that your site has not been updated in their index since then. Any content you've added in those two months is NOT YET INDEXED.
when googlebot access to your site, it takes a copy of your page to its own server. the name of this copy is cache. it's used run search queries