I assume you bought your phone here in NZ from Vodafone?
Here's a link to the Samsung NZ site which contains the manual: http://www.samsung.com/nz/consumer/mobile-phone/mobile-phone/smartphone/GT-I9100LKAVNZ/index.idx?pagetype=prd_detail&tab=support
You can browse the Android Market on your PC, might be easier to search around to begin with: https://market.android.com/
When you ready, open the Market application on your phone and install the apps you want. I wouldn't worry about a virus scanner, just stay away from unknown applications that may contain malware, read reviews on them first before installing.