The genetic code maps nucleotide sequences (DNA) to amino acid sequences (proteins). Every three bases (say AGT) maps to one amino acid. So you can literally re

The genetic code maps nucleotide sequences (DNA) to amino acid sequences (proteins). Every three bases (say AGT) maps to one amino acid. So you can literally read a sequence of ACGTs and decode it into a protein. A sequence that encodes a protein is called a gene. Almost all variations that humans have in their genomes (compared to each other or a reference genome) are tiny, mostly one base differences called single nucleotide polymorphisms (SNPs). These tiny changes encode who you are. The rest of it just makes you carbon-based organism, a eukaryote, an animal, a mammal etc, just like a whole load of other organisms.