Here are some links to YouTube videos to learn about the basics of DNA.
What is DNA and How Does it Work (by Stated Clearly)
DNA vs RNA (by Amoeba Sisters)
What is a gene? (by Stated Clearly)
What is a Chromosome? (by Stated Clearly)
Chromosomes and Karyotypes (by Amoeba Sisters)
Mutations (by Amoeba Sisters)
History of DNA
The DNA Double Helix Discovery (by HHMI BioInteractive; traces the history of how scientists figured out the double helix structure of DNA)
Rosalind Franklin
Rosalind Franklin: DNA’s unsung hero (by TED-Ed)
Rosalind Franklin: Great Minds (by Scishow)