Understand services at following websites. I have till now found them to be the best for starters
http://aws.amazon.com/products/ - Go through all the products and understand how it helps, how costly it is and when you should use them?
http://www.windowsazure.com/en-us/develop/overview/
- Go through the fundamentals i.e. Application Model, Deploying and
Updating Apps, Understanding Cloud Storage, Building Hybrid solutions.
Now
try and compare both these offerings. You will be surprised to see how
similar they are and they are even similarly priced. This will give a
good understanding of what is available in the cloud world. Once you
have done this you are on your own to go further in the area of your
sub-domain