In the opportunities module, I want to have a drop down of options X, Y or Z.
When user selects X: A, B, C D fields should show for user to enter information.
When user selects Y: G, H, I, J fields should show for user to enter information.
When user selects Z: K, L, M, N fields should show for user to enter information.
I have seen some posts that this is done through logic hooks. It is available with the free version and where do I find it. If it is not available, what are some workarounds?
Yes, logic hooks are available with the free version, as all features of SuiteCRM are.
You can find a Developer Guide online with a chapter on Logic hooks. The SugarCRM 6.5 documentation is also valid here.
However, for that kind of thing I don’t think you want a logic hook. The logic hook would act after saving the record, I think what you want is UI effect of showing and hiding fields. For this you would customize the display views and add Javascript.