Any tire you order is most likely a tubeless tire. If it isn't than it will say so. Concerning an Atv, tubes are used when/if you have a hole in the tire and a plug or patch won't due, a dry rotted tire that your trying to get some life out of still, tires with sidewall damage can't be patched or plugged so sometimes a tube can get you by. Or sometimes the rim itself may be to corroded, bent ,and or rusted and the bead will constantly leak so a tube will be used instead of bead sealer. Also if the tire is studed (think ice racing) than you may need a tube also..
So to answer your question. Just order the size tire you need and you will be good to go. Don't forget to get new valve stems also, there cheap and easiest to change when you already have the tires off..