I have registered a Free-Trial account on Azure site. In documentation I found: http://msdn.microsoft.com/en-us/library/windowsazure/dd179428.aspx that I need some Shared Keys to use APIs.
But where are they located on Azure Management Portal? I could not find them at all. Do I need a paid account for this?
If you open the Azure portal, click on the "Hosted Servcies, Storage Accounts & CDN" link on the lower left and then pick "Storage Accounts". Once you click on "New Storage Account" and create a storage account, you will see "Primary access key" and "Seconardy access key" on the right hand side if you select that storage account in the middle.
More info:
Creating a storage account: http://msdn.microsoft.com/en-us/library/windowsazure/gg433066.aspx
Viewing keys: http://msdn.microsoft.com/en-us/library/windowsazure/hh531566.aspx
Note, if you are meaning Shared Access Signatures for blob storage, look at: http://blog.smarx.com/posts/new-storage-feature-signed-access-signatures
Each storage account you create will have a primary and secondary key, which is ultimately used in the REST header for accessing tables, blobs, and queues. If you're using .NET, Java, PHP or any other language where you've found a library wrapping the REST API, you won't have to worry about constructing REST headers; instead, you'll just create a storage endpoint using your primary or secondary key.
Making this easier, the key can be stored in your configuration settings. Then, if you ever change your storage account (maybe one for development, one for production), it's a simple matter of changing your configuration settings instead of changing code.
FYI - these keys are created automatically when you create a new storage account. And... you may use either key, and invalidate / re-create either key at any time (which is great if, say, you share your secondary key with a 3rd-party service and then want to terminate your relationship with that service).
I'd suggest grabbing the Windows Azure Training Kit and trying out a few of the first exercises, as you'll see exactly how to reference a storage account this way.
