It's a combination of things:
-The fossil record is abundant. Don't be fooled by "popular" misconceptions like "the missing link". That's a lot like Adam and Eve... a myth. Transitional forms is what we look for, but technically, we're
all transitional forms.
However, there are
thousands of fossils showing direct change from one species to another.
Here is an overview/summary of what transitional fossils exist.
Here is a pretty decent, though a bit incomplete, list of transitional vertebrate fossils.
Some famous specimens include (but are not limited to)
Archaeopteryx (dinosaur to bird),
Australopithecus afarensis (primitive ape to human), and
Tiktaalik (transition from sea to land).
2. There is tons of genetic evidence. The best possible example is that we share 98.5% of our DNA with chimpanzees (think about that for a minute...
everything that makes us different from chimpanzees is contained in only 1.5% of our DNA). But what's even better is that, inserted in our DNA are things known as
Endogenous Retroviruses. What's really cool is, many of these viruses are
inserted into the exact same places in our DNA as they are in the chimpanzees' DNA.
3. Unintelligent design provides more evidence for evolution. Just look at humans alone:
-The
Recurrent Laryngeal Nerve
-The
Appendix
-The broken vitamin C gene
-The
tail bone
-The wiring of our eyes (it's backwards... without our brains, we'd actually see upside down)
-Other
vestigial structures in
the body
Just as some examples.
4.
The Double-Nested Hierarchy
Here... have this article of
29+ evidences for evolution.
See above.
Okay... please explain what you think the word "theory" means
Fair enough. I grant that my post was rather arrogant, but that was unintentional and I apologize. It is not at all your fault, but the statements you are making are not new to me... I've been participating in the Creation/Intelligent Design vs. Evolution debate for a few years now, both online and offline, and it's come to a point where I can recite certain tropes by memory... the post of yours that I originally responded to (and this one that I'm responding to now) contained a number of those tropes. And they are infuriating to me simply because I have to answer them over and over and over again.
Like I said; this isn't your fault. You and I have never discussed this before (at least... I don't think we have), so you can't know what I've heard and what I've not heard. My problem with a lot of the arguments your making is that they are so cliche. Honestly, it would take a couple minutes of Google searching to answer most of your questions.
In fact, I'll give you a site that should be your go-to source from now on whenever you have a question about Evolution:
Talk Origins
In my opinion, it is the absolute best archive of the whole debate; a debate, I should point out, that is not in any way, shape, or form, a
scientific debate. 95% of
all scientists (including engineers, medical doctors, social scientists, and so on)
accept the Theory of Evolution as a fact; including 99.5% of all
Life scientists (biologists, neurologists, anatomists, geneticists, zoologists, etc).
There is no controversy in science over the theory. There's a reason the trope "nothing in biology makes sense without evolution" exists; because it's true. You simply cannot make sense of the modern diversity of life without evolution.
Sure, you can explain the
number of creatures alive with intelligent design, but how does intelligent design explain the
evolutionary arms race?
Short form:
Cheetah evolves to catch gazelle, so gazelles evolve to run faster, so cheetah to run faster, so gazelle evolve to run faster, so cheetah evolve to run faster...
Just who's side is the designer on, anyways?
The controversy is purely religious and, by extension, political. It was settled in science by Darwin's "On the Origin of Species" (you should consider reading it, BTW... incrediblye dr and boring, but also
extremely informative... it took me a long time to get through it mainly because of my miniscule attention span...

... but I do not feel as if I wasted time reading it). It's just become so much more robust since,
especially with the discovery of the transitional fossils that Darwin predicted, and a discovery he never could have seen coming: DNA.
Some more books you may want to check out:
The Greatest Show on Earth by Richard Dawkins
Why Evolution is True by Jerry Coyne
The Making of the Fittest by Sean B. Carroll
Evolution: What the Fossils Say and Why it Matters by Donald R. Prothero
Your Inner Fish by Neil Shubin
I meant it when I said that there was no theory more well-evidenced in science than the Theory of Evolution.