Well, some random mutations will be harmful, some not have much effect at all, and some will be beneficial. The harmful ones are less likely to reproduce. The beneficial ones more likely to reproduce. That's how it happens.
There is no such thing as macroevolution. Or rather, macroevolution is simply microevolution, with a lot of steps in between. Every single fossil is a transitional fossil. When a gap is filed, it simply creates two more gaps. We are lucky that we have any fossils at all, but understand that evolutionary thery does not depend on fossils, although they are certainly helpful.
Here is a helpful article for you to look at: http://www.talkorigins.org/faqs/comdesc/
It's a worthwhile read and will take you through a lot of the scientific (and falsifiable) evidence in favour of macro-evolution.
Can you link to an article showing that some systems in our cells can't be there by chance? Is it in a peer reviewed journal? What does the scientific community say about it?
I don't know a lot about geology: how old do you think the earth is, and why do you think the current consensus is incorrect?