A lot of people that come into the store define themselves as “technology challenged”, meaning they have no idea what they need for a computer. They do not know what a GHz or a GB is. I will break this description down and try to simplify it.
2.5 GHz i5 (GHz stands for Gigahertz)
This is the processor. Think of this as the engine of a car (4 cylinder, V6, or a V8). The more GHz you have the more powerful your computer is. Think of the i5 or i7 as 2.0 liter or a 3.0 liter. The i7 processes information faster like a 3.0 liter engine gets more fuel to the engine faster. For most people doing basic tasks (email, surfing, creating documents) an i5 is fine. Professional photographers, musicians, film makers, graphic designers would want an i7.
4GB (RAM) (GB stands for Gigabytes)
I heard Hapy, the co-owner of Small Dog give a great explanation of what RAM is. Think of RAM as your desk, and think of programs as stacks of paper on your desk. The more RAM you have the bigger your desk is and the more room you have for these stacks of paper. If you have a smaller desk these stacks of paper start getting mixed up and cluttered. With more RAM your desk is larger and programs have more space. If you want to get more of anything get more RAM.
500GB (Hard Drive)
The Hard Drive is your “closet” The hard drive is where everything is stored. All your documents, photos, movies, etc… are stored in this “closet” Obviously, the more GBs you have, the bigger your closet, the more things you can store. Most documents take very little space while movies can be huge. You can buy an external hard drive to get more space or (at least on some Macs) you can install a larger internal drive. Music and photos can also take up a significant amount of space but a 500GB drive can hold 10s of thousands of pictures and songs.