I hope you know what is Google sitemap and what it is used for. If not, you might want to read about it at Google site. There are a plenty of services and scripts that allow to create a sitemap for your site and it is not so hard to create your own script for this (maybe I will show you the code some later). When it is created, you are welcome so submit it to your Google Webmasters section. But it is important to check it against errors before submitting and it is a good practice to have it valid.
You may need to study sitemap protocol specifications. Some characters should be escaped before putting them in an xml file. But how to check whether your sitemap is valid or not?
I am using an online service that allows to check the sitemap without uploading it – all you need is just to have it on your server. Let’s go to the page of Free Google SiteMap XML Validator and check our sitemaps. If something is wrong, you will receive a message where even number of error string will be shown. I greatly recommend you to study that web site – t has lots of useful information on sitemaps, more than I can write here.
Now you can be sure your sitemaps are valid. Smart IT Consulting also allows you to submit your sitemaps, so I consider it’s a great resource.