the hard drive is the memory of the computer. It is what will hold all of the programs, pictures, videos, and your operating system. This is a very important part of the computer, but for this one having a bigger hard drive doesn't help the computer to run better, so it's really just how much you're going to save on your computer. A terabyte is a lot of memory so for a normal computer I would recommend the 1 or 2TB hard drive. If this is a computer for gaming, you might want a 4TB hard drive or even a 6TB hard drive.

*a hard drive and a solid state drive both store memory. A hard drive can store a lot more for a lot cheaper, but the solid state drive can access it's data faster. If you want to store photos and documents to your computer I would recommend getting a hard drive. If you want your computer to be for gaming, I would recommend a solid state drive to download your games to so that they load faster. You can have both in one computer to save documents to the hard drive and games to the solid state drive.