I'd just like to know, if for a keyword, or a sentence, my website is in the search pages, and if so, where? Is there a way to do this?
The best you can do is use Google Webmaster Tools to see the top search queries and average position in rankings.
You can use automated tools as well but those are in violation of Google's terms of service.
I use Seobook's rank checker it's the best free one I've seen. There are also plenty of paid options out there that are good.
Also I'm not sure if this still works (it's a been a few years since I've tried it) but this article shows how to add approximate rankings to Google analytics http://yoast.com/track-seo-rankings-google-analytics/