It would be very hard to explain on here. Is there a deer processing place near you where you could go watch and learn. Happy to answer any questions about this, but you really need a visual aid. Just to cover some basics, you need a REALLY sharp knife. You have to be surgical about it. If you're using any downward pressure at all, you're gonna punch through and hit the guts. When you first start, make a tiny incision way up above the rib cage. Insert the knife upside down and cut back towards yourself to open him up as you work down over the guts. This keeps the blade facing away from the intestines, etc, to get the hide and skin opened up where you can start letting all the guts fall out and cut them away off the membranes.
Interesting question . When I shot my first deer, I told myself to treat it as a large rabbit, work slowly,with a very sharp knife, keep the blade facing up so you don't puncture anything . You just kind of keep removing things until the carcass is empty, careful not to cut yourself and wash your hands when done . I have an allergic redaction when deer blood dries on my skin. You'll do fine !