Stuxnet and driver

As far as I know, driver is used to be an interface between OS and hardware.

Both Duqu and Stuxnet use a kernel driver to decrypt and load certain encrypted files on the infected computer. The kernel driver serves as an "injection engine" for loading the files into a specific process, according to SecureWorks. "The kernel drivers for both Stuxnet and Duqu use many similar techniques for encryption and stealth, such as a rootkit for hiding files," the security vendor said in its report.

from:
http://news.idg.no/cw/art.cfm?id=A0D...F48A30CE1D5495

1-What is the kernel driver?

2-I read the article in wikipedia for DLL injection and it makes no sense, May someone tell me about it?What is difference between DLL injection and process injection?

Thanks in advance

DLL injection will infect all traffic coming thru it in the future, versus the immediately running process.

May you give me a simple code for DLL injection and explain more about it?