Oregon law requires chains on one tire on each side of the drive axle. This is typically the outside tire due to easy of installation. However, be aware that chains can be a problem on the outside tire on some Newells due to limited fender clearance. The pre 1990 Newells typically had less of a problem with this than 1990+ models.
California requires that the drive axle be chained. For buses and recreational vehicles, they require the inside dual rear tires be chained if possible and show all four dual tires being chained.
http://www.dot.ca.gov/hq/roadinfo/ChainRequire04.pdf
Washington State requires chains on one tire on each side of the drive axle.
Chaining up is not complicated but it is messy and requires effort to get them on. There are two methods people use. Some drape the chains over the tire first, then try to drive forward over them. The other method, which I find less frustrating is to lay the chains out in front of the tires you are going to chain, drive forward to put the tires on top of the chains, then wrap the chain around the tire and connect the two ends together. Make sure the chains are laid out straight without kinks before you start putting them on or they will be extremely difficult to get on.
Make sure you get chains for the proper tire size and lock them on tight.