You can walk into the wilderness from most any place in Yellowstone. The exception would be some of the thermal areas where you are limited in your access.
"Will a buffalo (bison) gore you"? It's always possible, but keep a good distance from them and you should be fine. We were enjoying a roadside rest area one day when a bull bison was very upset about something and came charging into the area. He charged towards us, but we were able to scatter into the brick restrooms and avoid a confrontation. He ran off into the forest, and we didn't see him again.
If you are hiking, I'd really recommend you carry and know how to use bear spray. It could save your life if you were to have a nasty encounter with a black or grizzly bear.
Here is some information on wildlife safety in Yellowstone:
Yellowstone Wildlife Safety Videos