You can use various plugins to create wordpress blog sitemap. I can suggest you one of the plugins i.e. google xml sitemap.
It is too easy. First search for a plugin name "Google XML Sitemap" in wordpress website. Download it and then install it to your website. Then create two files and rename these as "sitemap.xml" & "sitemap.xml.gz". After that upload it to your website with 777 as a numeric value of file permission. Now you need to active this plugin from your admin panel.
Sitmap is very important for wordprss. For this purpose we use XML use for create the sitemap but we use web tool master to upload.