New to Backcountry Skiing?
To safely enjoy the backcountry, there are a few things you need to get started - namely appropriate gear to get you up and down the mountain as well as avalanche training, equipment and the knowledge of how to effectively use it.
Regardless on what you call the sport (ski mountaineering, skimo, alpine touring, ski touring, etc) there is some required gear you will need to enjoy it.
Required Gear
A basic backcountry setup typically involves the following components:
Skis or Splitboard. Most any will do, but more expensive equipment typically saves weight and offers better float in the backcountry powder.
Skins. Modern skins stick to the bottom of your boards, and can be pealed off and reapplied repeatedly. More expensive and newer skins typically offer a faster glide on flat approaches, as well as better grip during uphill ascent. Make sure you get skins that fit your skis well edge to edge or else you may have trouble ascending anything but the flattest slopes.
Bindings. Telemark and Splitboard bindings are inherently built for backcountry touring, whereas you will need at AT (Alpine Touring) bindings for your skis that hinge at the toe if wish to use your downhill boots. Newer and more advanced equipment typically saves considerable weight and is easier to use.
Avalanche Equipment. At the minimum you'll need an Avalanche Transceiver, Shovel and Probe. Note that a Transceiver is a different thing than a passive Recco reflector that is sometimes sewn into ski jackets.
A quick note on snowshoes - generally speaking you will not be able to keep up with friends on skis + skins, but a "shoed" approach can work in a pinch or for short distances.
Avalanche Training
A Level 1 or comprehensive introductory class is critical before you get out into the backcountry. There are a few different training options available, though generally all good training should contain both classroom and field sessions.
The American Avalanche Institute (AAI). Level 1, Level 2, and Level 3 certification courses are offers through AAI at various points in the year. Level 1 starts at 24 hours worth of training and is 60% field based.
Gallatin National Forest Avalanche Center (GNFAC). Aside from a basic 1 hour avalanche orientation, GNFAC also offers a 20 hour basic avalanche training that is technically not a Level 1 avalanche certification, but does provide both classroom and field components.
American Avalanche Association (AAA). This organization does not actually offer it's own training courses, but does also contain a class listing for upcoming avalanche training in the state of Montana.