{Answer to the first question}:
-----Generally,DNA,RNA and protein satisfy the" Central Dogma".It can be simply described in this way:
[DNA--(transcription)--->mRNA---(translation)--->protein].
PS:in fact,there are three different types of RNA in eukaryocytes---mRNA,tRNA and rRNA.
PSP:Actually,mRNA is used to be a templet of translation.And we regard each three bases on the mRNA as one "codon" which can determine one particular amino acid.
tRNA is the compound which can get the particular amino acid to match the codon as tRNA has "anticodon" to specifically recognize the codon.In this case,the amino acids can be connected in order and eventually a polypeptide chain appears.
If this polypeptide chain continues folding into a substance having a 3D structure,it will be called "protein".
{Answer to the second question}:
-----One deoxyribonucleotide(the unit of DNA) consists of one deoxyribose,one phosphoric acid and one base(Adenine or Cytosine or Guanine or Thymine);
----One ribonucleotide(the unit of RNA) consists of one ribose,one phosphoric acid and one base(Adenine or Cytosine or Guanine or Uracil );
In that case,you can tell the differences between RNA and DNA.
PS:Generally,DNA is a double-strand molecule .In contrast to DNA ,RNA is usually a single-strand molecule.