Organisms trace back to their source code - DNA, which can be thought of as a blueprint. We have around three billion base pairs, the basic unit of DNA, in our genome. That’s about average. There are some animals and plants, however, with far more. Learn more about them from this video by Scishow.
We don’t know why some organisms have massive genomes, some with more than 100 billion base pairs. Sequencing so much DNA takes a lot of time, so it may just be that these organisms have replicated portions of their genome.
Our genetic material is organized into chromosomes. Humans carry two copies of those chromosomes, and while many other animals also have two of their own, plants can exist with far more; some even have eight copies.