Since GA is free it is a great tool used to track visits to your site. There are several WP plugins that you can use to automatically add your GA id to every page in your blog. I definitely recommend using a plugin for this.

GA will not tell you which keywords get you sales, but it will tell you what keywords get visitors to your site which is very important. Capitalize on those keywords and you are likely to get more visitors which will likely pan out into more sales.

GA does have Goal settings which allows you to determine when a particular action has occurred. For instance, you can set it on a thank you page. On one blog that I own, when someone subscribes to my list, they get sent an email with a download link (a page on my blog). I used a goal to be notified when this page gets hit.

Hope this helps.