The sitemap is one of the most important parts of a WordPress site.
Is the file wich contains all the URL you want to index in Google.
1. Download and Install the Google Sitemap Generator plugin.
2. Set it up. You can follow my screenshot to see how I have it:
(click to enlarge)
3. Add it to Webmaster Tools from Google. It will index your URLs faster and also will give you stats and reports.
Now you're ready to start publishing content 😉