The computer doesn’t have any real inputs that would allow it to read in values from the outside and use them to do some computations. The only data inputs are the ones used for programming the RAM. See this post for more information.
The computer has two possible outputs. One of them is the BUS output which isn’t an output in the traditional sense. The BUS is connected to an Arduino which displays the current value on it. This was done so the BUS can be monitored when stepping through the instructions.
The output register is what can be considered as an actual output of the computer. By using the OUT command a value can be moved into the output register. This value will then be output via the data lines coming out of the output register. Just like with the BUS the data lines are connected to an Arduino which will display their value on an OLED display.