Staying in the park means sleeping in a campground or in the back country. For those who enjoy their amenities, however, there are more posh accommodations in the countless towns one drives through on the way to the park. One can find anything from hotel rooms to chateaus with hot tubs.
camping
There are a number of campgrounds throughout the park, administered by the National Park Service (http://www.nps.gov/). Most offer potable water, dump stations, and firewood.
lodging
See above.
backcountry
Most of the park would be classified as back country. There are relatively few facilities outside of the campground, baring a few composting toilets in more popular areas.