DNA and RNA are abbreviations for deoxyribonucleic acid and ribonucleic acid respectively. This difference has to do with the fact that DNA contains a sugar called deoxyribose while RNA's sugar is simply ribose.
DNA has a double-helical structure while RNA is a single strand (resembling a single strand off a DNA's double helix). See the attached image for an illustration of this structure.
The bases of DNA are guanine, cytosine, adenine, and thymine. In RNA, by contrast, thymine is replaced by uracil.
Functionally, DNA is a kind of storage unit for genetic information. RNA uses this information to build proteins, copying it from the master copy contained in the DNA and converting it to a form the ribosomes can use.
