That's a great question! DNA, or deoxyribonucleic acid, is the genetic material of living organisms. This means that DNA is the heritable blueprint for the everything that makes up organisms (including you) from proteins to cells to whole organism form and pattern. DNA is transferred from parents to offspring through reproduction - in sexual reproduction each parent gives half of their genetic material - that's a big part of why you see variation among individuals. In asexual reproduction (like plants growing from clippings), the DNA of the offspring is identical to the parent.

DNA is chemically made up of two long strands of smaller units called nucleotides that are chemically joined together. There are four nucleotides (two pairs of two nucleotides) that make up DNA, and the order of these nucleotide pairs is the physical coding for everything that makes an organism. Sometimes, DNA gets miscopied or damaged (like by UV from sun exposure) and this can cause problems - like cancer. That's why we wear sunscreen - to protect the DNA in our skin cells!

There's a lot more information than what I've written you about DNA, so if you're interested in learning more, please contact me!