Please explain evolution.

I thought different combinations of genes would result in production of different enzymes. That's because a certain code in a gene would code for a certain enzyme, so even the slightest change would cause the enzyme that is produced to differ. That's like having two words, "too" and "two", which look very similar, and are different by only one letter, but they have different functions in a sentence (one's a noun, the other is an adverb), just as enzymes could be coded similarly, but aren't the same, and don't have the same function.

You haven't really mentioned too much about DNA sequence. Do you mean the changes in the DNA sequence cause the enzyme that is formed to change or do you mean changes in the genes?