That list is the tower itself, yes, which will have all the cables you need to put it all together. You've got the Motherboard/Processor being the core of your system, the RAM and the Hard drive, the disk drive and the power supply to power everything and the case to keep it all safe. With Windows 7 OS. The only thing you are missing is the software, it won't have Microsoft Office. It doesn't include a keyboard and mouse, if you are needing peripherals.
There are LOADS of step-by-step videos, walking you through putting a tower together.
As I said, with prebuilts, they do tend to cheap out on parts, like the Power Supply, which isn't a reliable area to cheap out on especially for a gaming system. Though for a cheap family PC I'd say it's possibly a more viable option. I'm afraid I don't have any suggestions for you on that front.
If you put it together yourself, you know exactly what's gone into your system and you have an idea of where you can upgrade in the future. For example, you can upgrade the processor to an i5, add in a second stick of RAM and get a 750ti, maybe a 760, and you are ready to play games quite well. At current prices that would be around an extra £300-350 upgrade.
If you think your system needs a graphics card, that will put the price up and you might want to consider an AMD option(possibly an APU considering AMDs rumoured/leaked roadmap), but I wouldn't have thought your listed needs would require a graphics card.