Off means four feet on the floor so it is usefull with a dog jumping on a counter/person or getting of the couch bed etc. The video link below is the start of an 8 part series that is pretty good one on teaching "off"
Something you need to keep in mind is you need to teach the the behavior before adding the cue. And a Cue without out any training is likely only to confuse the dog or simply learn to ignore it.