What is meant by the genetic code being nearly universal?

A lot of DNA is structural and doesn't pertain to any genetics while it only takes a small change to change something big. DNA mainly uses 4 different chemicals to change itself, not giving a lot of variety. Most animals share around 98% of the same dna with each other. Humans share 50% of their DNA with a banana. Pretty much everything shares the same double helix design as well. So a lot of genetic code looks similar.