Do you have InDesign CS3 already? If you do, using that is the most economical thing you can do until you get comfortable.
From that point, you have the option to try to find an upgrade to a newer verion on the open market (which carries a lot of risk of being counterfeit or unregisterable), or you can subscribe to the cloud (there's a first year discount, just extended, for CS3 and later users), or you can pay full price for a perpetual license to CS6.
Thanks for your response Peter. At the time of purchase InDesign was not a
part of CS3. Is it possible to upgrade to CS4 and how/where can I do that?
The only way you'll find an upgrade to CS4 is on the private sale market. The caveats above apply.