Evolution is a scientific theory.In the sciences, a scientific theory comprises a collection of concepts, including abstractions of observable phenomena expressed as quantifiable properties, together with rules (called scientific laws) that express relationships between observations of such concepts.
Let me explain the difficult words so you will understand.
Concept:
A concept is a cognitive unit of meaning—an abstract idea or a mental symbol sometimes defined as a "unit of knowledge".
Abstraction:
Abstractions may be formed by reducing the information content of a concept or an observable phenomenon, typically to retain only information which is relevant for a particular purpose.
Phenomenon:
In scientific usage, a phenomenon is any event that is observable, however commonplace it might be, even if it requires the use of instrumentation to observe it.
Quantitative property:
A quantitative attribute is one that exists in a range of magnitudes, and can therefore be measured. (Examples are time, length and weight.)
Evolution is NOT a hypothesis.Hypothesis:
A hypothesis is a proposed explanation for an observable phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose." For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous observations that cannot satisfactorily be explained with the available scientific theories. Even though the words
"hypothesis" and "theory" are often used synonymously in common and informal usage, a scientific hypothesis is not the same as a scientific theory. A working hypothesis is a provisionally accepted hypothesis.
Do I believe in evolution?You cannot believe in a scientific theory. A scientific theory is as described above used to explain a phenomenon. In this case why there is different kinds of animals.
If you were to observe evolution in reality, it would probably go like this:
http://www.youtube.com/watch?v=_sxh_L1LUNkAnd it does not explain how life began on planet earth. That is something completely different. And is described with a different theory.