Evolution is an overused term, it is used to describe an entire scientific field, the theories within that field, and the facts within that field...
As a scientific field: Evolution is a scientific field that deals with how species change. It does NOT deal with the following:
1. big bang
2. creation of galaxies
3. creation of planets
4. age of the earth
5. creation of life (it does not, in fact, claim that "life evolved from a rock")
Darwin postulated a "theory of evolution" that spawned an entire scientific field... we do not "beleive" in "darwin's theory" because we are not religious, his theory has been the foundation of modern field of evolution but is not taken verbatim... what is the field of evolution?
At the core of evolution is the OBSERVATION (which is as factual as the observation of the existance of gravity) that:
1. observation: creatures inherit their parent's traits: later discovered to be caused by DNA
2. observation: sometimes minor alterations are made: DNA can be copies incorrectly, if you do not beleive in that then you do not beleive in CANCER. (or in observable mutations in DNA) cancer exists, mutations exists. (which creationists sometimes claim, when they say that evolution only allows deletion and not creation, therefore it only allows micro and not macro evolution, terms they invented and sound incredibly stupid to anyone who knows what cancer is)
3. Logical statement (Math: statistics): traits (and DNA) more suited for survival or reproduction in a certain environment are much more likely to propegate (reproduce and survive)
All these observations come together in the following conclusions
Conclusion: Species are most likely to change to fit their current environment, barring that they are likely to die out. We call this process "evolution"... It is POSSIBLE but rare for an unsuited species or trait to survive, and realistically only happens in the "short term". (since eventually their shortcomings will catch up with them).
The conclusion is the ONLY possible conclusion based on those factual OBSERVATIONS, this leads to actual THEORIES. theories such as "these creatures evolved from these common ancestors" and and "humans evolved from a common ancestor as the great apes", and so on. While those theories assume the existance of evolution (a fact), they are actually focusing on the individual history of a species, which are theoretical and hard to prove, but are backed up by evidence such as the remains of ancient humans, their dna, the dna similarities with apes, and so on.
The field of evolution can include eugenics, genetic engineering, observable evolution of all individual species, etc. It is a growing field with new information, but the new information does not. Invalidate the core observation that there is a process of evolution (just like new information in physics does not invalidate the existance of gravity... we might change the explanation as to why or how, but we can observe it is there).