Can't keep the wood burning in stove. How does the buck stove take in air?

To burn properly, it needs proper combustion air and proper draft. Draft is effected by the size and height of the flue the appliance is connected to and by how much combustion air is available. The appliance flue connection should not be reduced to fit a smaller chimney size. That is, an 8" flue should not have an 8 x 6 reducer to vent it into a 6" chimney.

The wood you are burning could contribute to a poorly burning fire. To burn properly, the wood needs to have been "seasoned" for a minimum of 1 year or close to it. Two years is even better. "Green"
or freshly cut wood contains an unbelieveable amount of moisture in it and a tremendous amount of the heat is wasted just "preheating" the wood to the temperature that causes it to release gasses for ignition.

I don't know the style or model of your Buck, but all wood burning appliances should have combustion air dampers of either a sliding design, rotating round design or hinged design with handle at the bottom front of the firebox. I'm sure there are some fancy new designs that have air piped in from outside the structure.

Every wood fired stove, fireplace or furnace has its own idiosyncrasies and its up to the user to determine what's required for making it operate as designed.

Wood burning fireplaces are not meant to be controlled other than some have control of where combustion air comes from, in house or from outside. This will have some effect on how much warm air from the house will be used for combustion and wasting heat out the chimney.
Wood burning stoves should have an adjustment for how much air is allowed in the firebox for combustion. By throttling the inlet air you can control how fast your fire burns the wood. If you close off the inlet air completely, the fire will go out. Fine tuning will allow you to control the amount of heat given off and how long before more wood needs to be added. The flue damper can also be throttled to limit wasted heat from going out the chimney but requires careful monitoring to avoid backing smoke into the room.