In terms of computer speed, efficiency and electricity cost, what do these terms used for computers mean?

I'll answer your second question first. By today's standards your computer isn't very good frankly, though it depends really what you use it for. I recommend upgrading to Intel's new icore series processors, either the i3, i5, or i7. The i3 is a mainstream processor meant for general computing. The i5 and i7 Quad-Core variants are meant for more graphically intensive tasks, particularly the i7. It's intended for gaming. As far as RAM is concerned, I can tell by the RAM that you listed there that you're either running an older operating system (XP) or you're attempting to run a newer OS without enough RAM. I recommend Windows 7 (which is a 64 bit OS and will require at least 2-3GB to run effectively). If you plan on purchasing an i7 then I recommend at least 4GB of RAM. Your graphics card could definitely use an upgrade, though it isn't truly necesary unless you plan to play games with it or spend a good portion of your time viewing HD content. I'd recommend Nvidia's Grpahics cards. Which one is up to you, I don't know what you plan to do with this machine. Your Hard drive is excellent, unless you require more space, that should do for most purposes. Good Hunting, I should warn you though that a complete upgrade like this could possibly be costly, perhaps it's just best to invest in a new computer.