DNA contains a double helix, but following the process of transcription, you are left with RNA that is composed of a single helix.
Your follow up question is a bit more challenging. RNA is essentially the intermediate between DNA and protein, but it is less "shelf-stable" than DNA or proteins because it doesn't have the protection of the double helix. RNA is a necessary intermediate that is formed when DNA "unzips" for a short period of time. RNA forms for a short moment, is translated into amino acids that comprise proteins, and then the RNA is broken down into its component nucleic acids.