i want to track sales for an ecommerce website where there is lots of product available and each product has unique price. This is very different by using goal.
Not really sure from your question what you mean by 'using goal', but I'd guess conversion tracking is what you need. Sign in -> 'Reporting' tab -> Conversions. It's pretty easy, just set an action name and select tracking purpose as purchase/sale. Create the conversion and just follow the instructions to paste the code into your website. I'd also recommend utilising google analytics as much as possible to find out which of your pages are effective et cetera. Apologies for the brief answer, I'd go into more detail but I'm rushed off my feet. Throw a message over and I'm more than happy to help you in a bit more detail.
There is ecommerce tracking function provided by Google Analytics. You can link your adwords account to it. Ecommerce tracking allows you to track every detail from your sales. It can track shipping, tax, individual product (including the Item #, Product name and price), each invoice sales etc. More details here: http://www.google.com/support/googleanalytics/bin/answer.py?answer=55528