You will also see that CPUs are rated in terms of speed. In general, the higher the speed rating, the faster and more powerful the CPU will be. The faster ones will obviously be more expensive. A good rule of thumb is to purchase a computer with a CPU that is a step or two below the fastest speed. This way you get a powerful computer without spending top dollar.
Storage comes in two forms, internal and removable.
The hard drive is your internal source of storage and is a necessity. A 16GB hard drive gives you room to install the most intensive applications with room to spare. External drives include Zip and Jaz style drives. A 100 MB Zip drive can come in handy for transferring and storing large files, but a 2 GB Jaz drive are useful for making backups. DVD drives are becoming common and will likely replace CD-ROMs in the future.