what is done differently in setting up a single speed and fixed?
It can be both. Fixed gearing is usually associated with Track bikes with no brakes. Resist pedal to slow. Track bikes are single speed, We can also get SS with a disc brake. What is your question??
Wheelies don't pop themselves. (from a QBP fortune cookie)
Any standard freewheel hub or cassette hub can be made into a single speed. You either put on a single speed freewheel (or just use one gear on a normal freewheel) or use spacers to fill up the cassette and have a single cog on that.
A fixed gear should use a specific fixed gear hub. They have two separate threads on the gear side, one for the cog and a smaller, reversed thread for a lockring. It is possible to make a normal freewheel hub into a fix by jerry rigging a lockring, but there are safety issues. It's also common to see "flip flop" hubs where one side is made for fixed and the other for single speed freewheel so you can easily go back and forth. Or you'll see hubs that are "fixed" on both sides so you can have two different sized cogs for different road conditions.
You have to have brakes on a single speed. You don't "have" to have hand brakes on a fix because you can stop yourself using the pedals. But lots of people put at least a front brake on a fix when used for street riding. Even someone very skilled at braking using the pedals on a fix still can't stop as well as someone with handbrakes since it is the equivalent of just having a back brake (which is typically about half as powerful as a front.) And it takes some practice and skill to even achieve that level of braking with just the pedals.
Single speeds are really just normal bikes without multiple gears. Nice that they're a bit simpler, lighter, etc. But fix is a bit different riding experience. I recommend trying it. But it's not the most practical for commuting, etc.