Give
wikipedia a try. I've looked at the Hip Hop and the Jazz article for example and they are a very interesting read.
I personally think that musical genres are best defined by a few key artists. My exposure to these genres can be considered limited so I can only suggest some who have made it to commercial fame.
AFAIK there is no useful distinction between Rap and Hip Hop. Listen to Snoop Dogg, Dr. Dre, Cypress Hill, MC Hammer.
I think with R&B you mean "Nu Soul" stuff. (Which I personally
hate dislike). Try Destiny's Child, Aaliyah.
I have never heard of blue
Jazz is definitely very distinct from the others. It is much older and is considered to be the first musical genre developed in the USA. Usually it is performed by musicians playing an instrument.

Try Miles Davis.
You'd have better luck asking me about genres of electronica.