Windows Azure SQL Server is basically the same thing as SQL Server. You can create databases, write queries, and perform other actions like you would with a "real" SQL Server. You can even mirror a SQL Server to Azure. However, there are some differences because of the fact that it is cloud-based. My suggestion would be to start with an overview of Azure:
http://msdn.microsoft.com/en-us/library/windowsazure/ee336279.aspx[
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Once you get through that, you should understand how Azure SQL Server fits into the mix. From there, you can determine whether a local SQL Server or Azure SQL Server is a better fit for your needs.