I thought my explanation was sufficient but I will explain it in more detail for you.
It is called a “phylogenetic tree” and it shows the evidence (one data point out of many thousands) of common descent from DNA comparison of a segment of DNA common to all the species. Each species has a different sequence there, and the most “parsimonious” tree arranges the similar with the similar and the divergent further away.
This tree, unlike many others, includes the actual numbers of DNA differences that they were counting for this particular data point (there have been several methods and sequences used and all derive the same tree).
This particular tree shows that humans and chimps are closer to each other than either is to a gorilla. If you are counting the differences would be...
Human-chimp= 42+28 = 70 DNA differences
Human-gorilla=42+16+42= 100 DNA differences
chimp-gorilla=28+16+42= 86 DNA differences
This is the pattern we see repeated over and over again. Every tree we make based upon data shows that humans and chimps are closer than either is to a gorilla.