When google start ranking a page

when google start ranking a page when it is cached or when it is firstly crawled ??

more specify your question.

i dont understand your question and i think you should rephrase it.

i mean that my page is showing in the gogle results but when i take a specific sentence from that page for viewing it is not able to show me ..
not able to undertsnad think you made apost in blog a new one and that is updated within 1 hr in google - page is not cached yet but when i put the url to google search it showing url but when i take a sentence from that part of post which seems to be unique it is not showing in results.. does google ranks page after caching or what.

Good question, I believe that the actual web page can start ranking for specific keywords and phrases once it's been "indexed". A cache is probably required for on-page long phrase searches.. like 2 full sentances. However, you could simplely do a private SEO test yourself to check this out.

so is there any difference between caching and indexing

http://www.googleguide.com/cached_pages.html
http://www.googleguide.com/google_works.html

Not necessarily either...

Your website can be crawled and cached without being ranked in the SERPs. The same cannot be said the other way round however.

I'm guessing, it will be first crawl. Why this thing matter to you by the way?

If you want it indexed faster then get a backlink from a frequently spidered site.

Most social bookmarking sites will do the trick.

Google is indexing my site already, and I get traffic from the organic ( almost 50 daily) and my ranking is still 0.
I want to know if I'm doing anything wrong that my ranking doesn't go up.
Because I have other sites that get less traffic and they rank 2 or 3.
Please help me.
Thank you.

If you are referring to Toolbar Pagerank, it has nothing to do with how much traffic you get. It's only an indication of links to your page, not your site. Sites don't have Pagerank, each individual page on your site is given a Pagerank.

Google does not disclose your current Pagerank on the Toolbar it only shows a snapshot of how you ranked at some point during the last few months.

I believe it would be wise to try to ignore the little green line. It has been known to distract folks from promoting real traffic to their site.