Re: What is RNA in terms that I can understand?

Hopefully, the following is of use - they are drawn from Asimov's 
Chronology of Science and Technology:

Nucleic Acid (1869)
  The classification of foodstuffs into carbohydrates, fats, and proteins
seemed to be satisfactory for the early part of the 19th Century. However,
in 1869, a Swiss biochemist, Johann Friedrich Miescher (1844 - 1895) was
able to isolate a substance from the remnants of cells in pus that did not
belong to any of these three classes. It contained carbon but also had
both nitrogen and phosphorus.
  Miescher took his new discover to fellow biochemist, Felix Hoppe-Seyler
who independently investigated the matter. When he discovered a similar
substance in yeast, the discovery was announced. Since the material seemed
to originate in cell nuclei, it was called "nuclein" at first, and later,
because of its acidic properties, the name was changed to "nucleic acid".

That is, Miescher and Hoppe-Seyler had isolated and characterized a 
fragment of a cell that appeared to be associated with the nucleus, 
appeared to be an acid, and appeared to not be any of the previously 
identified cellular fragments.

Purines and Pyrimidines (1885)
  Since the nucleic acids had been discovered by Miescher, little had been
done to determine their molecular structure. The German biochemist,
Albrecht Kossel (1853-1927) took up the challenge. He got rid of the 
proteins associated with the nucleic acids and worked on the material 
itself.
  By 1885, he had obtained substances from it that included the double-
ring purines and single-ring pyrimidines. He isolated two purines,
adenine and guanine and three different pyrimidines, uracil, cytosine,
and thymine. He also decided that a sugar molecule was present but couldn't
tell which one.

So, by 1885, the nucleic bases were identified. However, because Kossel
was working with whole cell extracts, he did not distinguish the source
of these bases as either RNA or DNA - simply the constituents of nucleic
acid.

Ribose (1909)
  In 1909, the Russian-born chemist Phoebus Aaron Theodor Levene (1869 -
1940) extracted a sugar from nucleic acid and identified it as "ribose".
It is a five carbon sugar, forming a pentagonal ring. Not all of the 
nucleic acid molecules possessed it, but those that did came to be known
as "ribose nucleic acid" - abbreviated RNA.

Thus, the name "RNA" comes from a literal description of the content of
the material. It is a series of nucleic bases linked to a sugar unit 
(sugar units are linked as phosphate esters). DNA or deoxyribose nucleic
acid was the other form or "not ribose" form of nucleic acid and it wasn't
isolated until 1929. It wasn't until the mid-1950's, with the discovery
of the double helix by Watson and Crick, that the importance of DNA and
RNA to life were discovered.

In essence, DNA is the recipe for all of the proteins and other molecules 
that make up our bodies. RNA is the chef who reads the recipe and makes the
compounds. That is a crude analogy for what RNA is and does, because there
are three forms of RNA and they all play different roles, but the purpose
of RNA is to take genetic information from DNA and translate it into
proteins, which subsequently fold-up to become enzymes, which make all of
the compounds from which we are formed.

Hope this helps.