They work by establishing arc plasma between the nozzle and the work. The plasma is conductive.
Yes, compressed air is now the common driver.Inert gases were used initially and still are on sensitive material.
220VAC hookups are standard foo home shops. The swarf doesn't have the thermal "memory" like oxy torch, plywood could suffice as a bench. There will be charring.
The "pierce" rating of the machine is a good indicator of capability. If the intention is cutting non-ferrous greater capacity is required vs. steel only.

Oh -- there IS air involved. I wasn't sure. Sounds like that will be something to use in the far far future.
My hubby isn't too happy that I'm taking over his garage with my "new hobby" ~~ LOL

The compressed air requirement is modest for the type machine you would likely get. Any basically equipped garage compressor probably fills the bill. Hubby might find the cutter VERY handy.

If you're interested in seeing what plasma can do with intricate work or repeatable work, go to www.torchmate.com
They're small units for small shops or craftsmen who sell the work at craft shows.

Here is a link that might be useful: Torchmate

OMG, you will love one. There is so much you can do with one. I have a miller plasma cutter.

Hey there Gretch and Toomuch whats new??Gretch what Miller do you have my husband is interested in getting a small hobby one ...whats good anyone out there??

Hey Annie ...... nothing new -- I'm just dying for the "big boy tools" ... *sulking* .....