Hard Drive: The hard drive is the main storage memory of the computer. Hard drive storage is measured in Gigabytes or GBs. In computer talk this is called a gig. The higher the GB of the hard drive the more total storage you have.
Random Access Memory: This is abbreviated as RAM. RAM was measured in Megabytes, or MB. New computers are now available with 1000MB which is a gigabyte. RAM is the active memory a computer has to process or manipulate data. The higher the RAM number the more memory is available. More RAM will allow you to do more things on the computer simultaneously and faster. Having too little RAM is a common cause of computer freezes or crashes. If this happens then you use the alternative RAM definition, Rarely Adequate Memory.
The two kinds of memory or storage confuse some people. A useful analogy is to think in terms of books. The hard drive storage is the total data you have available. It is like all the books you have on the shelves. The more shelves you have the more hard drive storage you have. The RAM memory is the book you have taken off the shelf and are currently reading. RAM is like your desk, the bigger the desk the more books you can keep open on it.