This is an excellent site for explaining RNA. I looked through it and I have copied what I found to be the best info for you, but if you need further explanation you can just go and look around on the site. The info below was copied and pasted from wisegeek.com. Hope this helps, and good luck! :) P.S. Also, if you don't understand some vocab, dictionary.com will totally work for you.
Ribonucleic acid (RNA) is a chain of nucleotides present in the cells of all life. RNA has a number of important functions for living organisms, ranging from the regulation of gene expression to assistance with copying genes. Severo Ochoa, Robert Holley, and Carl Woese all played critical roles in discovering RNA and understanding how it worked, and more research on RNA is constantly being performed.
Many people are familiar with deoxyribonucleic acid (DNA), a nucleic acid which is often referred to as the “building blocks of life” because it contains the genetic material for its parent organism. RNA is equally important, even if it is lesser known, because RNA plays a critical role in helping DNA to copy and express genes, and to transport genetic material around in the cell. RNA also has a number of independent functions which are no less important.
This nucleic acid plays a role in the synthesis of proteins, the duplication of genetic material, gene expression, and gene regulation, among other things. There are a number of different types of RNA, including ribosomal RNA (rRNA), transfer RNA (tRNA), and messenger RNA (mRNA), all of which have slightly different functions. Studies on these different types of RNA sometimes reveal interesting information. rRNA, for example, undergoes very few changes over the millenia, so it can be used to trace the relationships between different organisms, looking for common or divergent ancestors.
DNA plays a role in the synthesis of RNA. Essentially, DNA contains the blueprints for making RNA, so when the cell requires more RNA, it pulls up the necessary information in the DNA and gets to work. This process is known as “transcription,” referencing the fact that the information is basically copied from one molecule to another. Some very sneaky viruses, like HIV, are capable of reverse transcription, which means that they can translate RNA into DNA. Drugs which target such viruses often focus on the reverse transcription capability of the virus, working to block it so that it cannot perform this function.