Hi KAYEM6,
A Pot, or potentiometer in full, is basicall a rotary knob. Like for example a volume knob on a stereo system, that you turn either clock- or counter-clockwise to turn the music louder or less loud.
The BU0836 is a small, ready made, circuitboard, that you can use to wire pots or knobs to, to have axis and buttons to build your own joystick, or indeed, shipsim controller. It is the "brain" of the controller, that way.
Your pots and knobs would be wired to this unit (and each other, in places) and the unit will be connected, via USB, to the PC...and then the circuit board tells the PC what you are operating. You can assign the axis (pot movements) and knobs as you see fit. Thus you'll end up with a custom built, fully programmable 'joystick'.
If you have some materials laying around that you can use to make the 'body' of the controller, then you probably only need pots, some knobs, and the BU0386 unit. I guess you can make one for about 50 to 70 Dollars (the BU0386 costs about $35, the rest is fairly cheap). Maybe a bit more if you do not have some spare wood (or something for the casing) lying around.
I am building one, and although it's on the shelf for a bit whilst I am busy with other things, I have spent about 45 Euro's in materials and I have everything I need. So yeah, 45 Euro's, not bad for a custom build controller. Now it's just a matter of putting it all together. And for that phase, one would obviously also need some basic skills with several different tools, and one would need to have (or borrow, or rent) some tools too of course. But it's relatively easy, really. It all depends how far you want to go, and how good you want it to be. You can buy second hand real gear, but that's really really pricey, usually. So this is a nice way to do it, and not expensive.
Regards,
Fred
* Edit * Typo