I'm quite new to technical stuff.
Can anyone answer this question?
Can you have dual GTX 670?
If so, how ?
You need to go do some research if you have to ask this question. Spend some time on Wikipedia, the forums here at Tom's, and in general do some Googling. I'm not trying to be rude at all, but we can't give you a Computer Science 101 course here. Well we could but I'd want to get paid.
Yes you can use 2 gtx 670s in the same build . you will need a powersupply that can run both of them and the rest of your system,a good case with high airflow, a motherboard will 2 8x or 2 16x pci exspress lanes,and a sli cable. http://en.wikipedia.org/wiki/Scalable_Link_Interface
As it will say ^^^. You can mix vendors but not models,that mean if you have an asus 2gb 670 and a msi 2gb 670 they can be combined as a dual card solution but if you have an asus 670 and an asus 680 those can not be combined. AMD also has a dual gpu system called crossfireX. Most people just refer to it as crossfire.The same basic principles apply you can mix vendors but not models.All though i do not recommend mixing vendors even if it can be done.