Imagine you have the text of a book in a word processor. You can change the text by typing new words or deleting ones that are there. You can also change the font, size, alignment, etc. The latter category of changes does not alter the words in the text, but it can affect how that text is interpreted, which parts of the text a reader focuses on, etc. The difference between a genetic alteration and an epigenetic alteration is conceptually similar. Genetics is changing the "text" of the genome while epigenetics is changing aspects of the genome that affect how that "text" is interpreted and used.