google analytics?

can someone tell me the exact plugin i should use to put google analytics on my wordpress pages?

Try this one:

http://ww.wp.xz.cn/extend/plugins/google-analytics-for-wordpress/

also what is the diff between page impressions and visits?

As long as the terminology hasn’t changed in the last few years, visits are when someone actually visits a page, and impressions are when something is loaded within a page.

So, a page on your blog would have a visit count, where as an image within that page would have an impression count.