You just put all the parts together on a site and they will build it for you.
But do you think this is good for a starter game pc?
No, they don't put the part together for you, but they do have prebuilt systems as well.
Ok, out of those websites ebay has the best deals. I have what I think are the 3 best systems for your budget, I will explain your options then you can decide:
1. This system has the most powerful graphics card of the 3 and will give you the best graphics performance:
http://www.ebay.de/itm/Gamer-PC-Int...439627?hash=item43d66f7d4b:g:cH4AAOSwyQtVv2rF
2. This system has the most powerful cpu of the 3, but has a graphics card that is a little less powerful than option 1. If you are planning on upgrading your graphics card in the future then this is the one I would buy, as you would end up with a better cpu and graphics card.
http://www.ebay.de/itm/AUFRUST-PC-I...685447?hash=item4885197d07:g:HA0AAOSwo0JWKjWh
3. This one is my personal favorite of the 3 because of the potential to overclock the cpu as its a K version. When it comes to gaming, looking at benchmarks it seems the the 6700 and 6600k are pretty much equal, but if the 6600k was overclocked then it should surpass the 6700 in gaming performance. It comes with the same graphics card as option 2.
http://www.ebay.de/itm/AUFRUST-PC-I...265710?hash=item2ca3899c6e:g:9PcAAOSwo6lWKjWM
IMPORTANT: Read the ebay listing carefully, note that option 2 and 3 do NOT come with hard drives and do NOT include an operating system. If you scroll down the pages you will see optional extras, so hard drives, operating systems and other options can be added at an additional cost.
Summary:
Option 1. Best graphics performance
Option 2. Best cpu, but little less graphics performance
Option 3. Would be the best cpu if it were overclocked, has the same graphics performance as option 2.
Option 1 comes with windows 7, for the other 2 otions you would need pay an extra 29 euros for windows 7 or 99 euros for windows 8.
Let me know if which system you are interested in, if any, so I can suggest which extras you need to get. All 3 options should end up costing about 800 euros.