Understanding Evolution

Scientists are very careful about the terms they use to describe what the lay person may call "theory". The layman's term "theory" usually corresponds to what a scientist would call a conjecture (if not backed by evidence) or a hypothesis (if backed by evidence). So the "theory" that " Easter Bunny exists" is a conjecture and “Sky is blue because of blue fairy dust in the air" and "Sky is blue because dust particles in it reflect (scatter) the blue part of the spectrum" are two competing hypotheses. None would be called a scientific theory, though. A collection of hypotheses become a scientific theory when they are validated using the scientific method. I.e. scientist make predictions based on the hypotheses and try to disprove them in an iterative process. Those that are disproved are discarded, those that aren't disproved are refined and may become part of the theory. Note that evidence cannot "prove" a scientific theory, it can only "support" it (or, of course, it can disprove it).

There are actually lots of very good resources on evolution online. The Understanding Evolution site is a wonderfully readable resource about the science of evolution.

One problem is that evolution is often taught on its own instead of being taught as part of life science material. And it's often taught by people that don't understand it (for example, it doesn't say that we evolved from apes, but it does say that humans and apes had a common ancestor). The theory of evolution is fundamental to all life sciences (drug resistant bacteria is an example from medicine) and not just the obvious zoology and botany. And even there, for example, the view of classification has changed from the Linnaean taxonomy I learned in school to the more current Phylogenetix taxonomy. And that, by the way, is another example of science at work: continuously re-examining underlying hypotheses and applying new ones as new evidence (such as the discovery of DNA) becomes available.