A tristate buffer isn't complicated. Ideally, it looks about like this:
simulate this circuit – Schematic created using CircuitLab
(I've included BUF1 and BUF2 mostly to illustrate that the input impedance can be different from the output impedance that is coupled to/through SW1. But you can also just mentally ignore them for some thinking purposes, if that helps you.)
Where SW1 is controlled by BUF2 (with some unknown input impedance.) Note that when SW1 is in position TRI, that the output floats. That's also known as high impedance because it isn't connected to anything. (In practice, nothing is so perfect as that, so there will be some very small conductance present.) When SW1 is in the ~TRI position, then the output will have the conditions of BUF1's output (impedance, voltage source, etc.)
In logic, of course, the input will be allowed to be whatever signalling is used for a "0" or a "1" and most practical designs will have BUF1's input impedance as high as possible so as to reduce the loading on whatever is driving it. (Similarly, BUF2's input impedance will also be as high as practical.)
There is also something related called an open-collector or open-drain output. These look more like the following case:
simulate this circuit
Note that in this case the logic value at the input controls SW1. (In the first case above (the first schematic), the input logic value doesn't control SW1.) The output will either be a low impedance output "0" or else a high impedance "1". These are also useful to know about. You can see their output as either "0" or "tristate."
The tristating control input impedance should be as high as practical. But even that is a matter of circumstances. I suppose if one is trying to drive it with a 50 ohm coax/driver situation, you might prefer that input to have a matching impedance. (Don't know of any situation where that happens, though.) The input itself (first circuit case) normally also has as high an impedance as possible where logic states are involved. Though if the input were to be an analog signal of some kind then it might be best to completely remove BUF1 somehow and actually just have a wire to pass along that analog signal as accurately as possible.