I'm very new to web programming (I do desktop development professionally). I want to learn more about web programming, especially using the jQuery library. I see references to jQuery UI and jQuery Tools; I even find that there is some controversy surrounding these.
What is the relationship between jQuery and jQuery UI/jQuery Tools. Is one preferred over the others? Are there any references (besides the respective home pages) for using these libraries?
There is no relationship between the two libraries except for the fact that they are both built on top of jQuery.
In my experience, both libraries work very well for the set of feature that they provide. You need to have a look at the feature set on the home page and decide on what you need, then make your choice.
As for documentation, I would expect you to find more documentation on jQueryUI, as it is used by many people all over the place (I don't have numbers or anything, but my guess is that jQueryUI is used a lot more than jQuery tools). The documentation on the jQueryUI website is amazing and provides examples for every component.
I use jQuery UI a lot because of the drag and drop function, that is not present on jQuery Tools. Some time I use jQuery Tools for the tooltip that is not present on jQuery Ui. So I would say that you would need to check what you need before picking one.
Both have the option to build custom packages with what you need to make them lighter.
In both cases, to learn them the demos are a good place to start, documentation its quite good.