Snort it the first time. That is assuming you get powder. If you get tar, it is probably easier to smoke it. However, powder is what I always got and snorting it is wonderful for the first time.
It's hard to say how much H to use. Start by sniffing a small line (smaller than any line of coke you see people snort) and take more at least a half hour to hour later on if you're not feeling as high as desired.
Pure heroin is white; most drugs are white when pure. Technically colorless, but colorless shows up as white to us most of the time.
Most heroin is cut though, and you're probably going to end up getting some form of cut heroin.
Besides, you think an OC is all oxycodone? nope.