this may sound kinda crazy.does anyone really know the difference between ALEXA and google analytics.and if it is recommended to use both in website
From what I know, Alexa is a company that publishes data about websites (amount of traffic, demographics, etc.) publicly.
Google Analytics data is not public. You install the script (customiZed if needed) and only authorized users get access to the data and there is a boatload...what queries and what positions you showed up for, actual traffic, page flow, user data and more.
I use GA to gather data for optimization. I have also uploaded an Alexa validation page/code/tag to my server so that I am verified in their index and can obtain whatever additional data they might offer...although I don't know what that'd be yet, my website isn't highly trafficked enough to have much Alexa ranking.
If that is what you mean, yeah, use both.
The difference between Alexa and Google Analytics is huge! Alexa is estimation service. Mostly, it does not know exact numbers, but it collects statistics and gives you the traffic estimation.
Google analytics lets you get detailed statistics about YOUR site. But it will not let you snoop at other websites.
In our days, Alexa does not give you traffic estimation - instead, you get Website Traffic Rank. You may use a complimentary service, which converts Alexa Rank to number of visitors: http://www.rank2traffic.com/
You may be also interested in a very useful website SimilarWeb: http://www.similarweb.com/.