The DNA is doble stranded in a double helix structure. There are 5 nucleobases (adenine (A), cytosine (C), guanine (G), thymine (T), and uracil(U)), only the first 4 are present in the DNA whilist the U substitutes the T in RNA.
The DNA has deoxyribose sugar while RNA has ribose sugar, that's what gives the doble stranded and single stranded form respectively.