Hello and welcome to the forums!
Let's look at the RAM first.
RAM, Random Access Memory, is used for multitasking. More RAM = more background applications.
Personally, I would go for 6GB RAM. The more the merrier. However, the computer will still work great with only 4GB. Windows 8 only requires 2GB of RAM.
Now the storage medium is where it gets interesting.
The cheaper option just has a 500GB hard drive. You can't go wrong there. 500GB of solid disk space.
The more expensive option has a 500GB HDD + 24GB SSD. This is known as a Hybrid Drive - essentially merging HDD and SSD technology.
HDD = Hard Disk Drive, and SSD = Solid State Drive - much like USB flash memory sticks.
This Hybrid drive actively monitors your data and automatically puts your most frequently accessed data onto the SSD for faster loading times.
SSDs read and write much faster than HDDs. By placing, for example, your operating system on the SSD portion of the drive, you can load the Windows faster than if you were loading it from the Hard Disk.
Your larger files, such as movies or music, would be placed on the HDD portion of the drive.
I know I said I would go for the 6GB RAM option, but you can always add more RAM. It will be considerably more expensive to buy a new Hybrid Drive.
If you can spare the extra change, the Amazon one would be a better buy.
If you are ever unhappy with the RAM, ~$40 would get you an additional 4GB.