This command is useful in all aspects of your hound's life. We started using it out walking to stop before we crossed the road. But is has had many uses and can come in very handy. It is also quite simple to teach and can be expanded on with a bit of effort.
One night last winter one of our hounds went to get off the couch, however they were wrapped in a blanket and were about to drag the blanket across our coffee table and wipe out everything on it. I said "Stop" quite by reflex and was very pleasantly surprised when she stopped with front feet on floor and back feet on couch. Allowing me to untangle the blanket and save the contents of the coffee table.
To me 'stop' means plant your feet and don't move until I say you can but note this is not a 'stay' command. To start with when you are out walking whenever you stop, to cross the street or open a gate etc, and the hound has stopped and has a loose leash, say "stop". When you are ready to go use a release word like 'let's go' and then start walking again.
You stop, hound stops, say "stop", treat, "let's go".
It helps with the hounds learning to have some treats in the beginning so you can communicate to your hound exactly when they are doing what you want. Plus you become much more rewarding to listen to. 'Let's go' doesn't need treats as the treat is the walk keeps going.
It is really important in the beginning to only say 'stop' when the hound has stopped with all four paws still. You want your hound to associate his behaviour with the word. DO NOT say "stop stop stop stop" as your hound is dancing around you, 'stop' will very quickly mean 'dance around me'. If you have done this already then use a different word for this training - 'halt' or 'still' are a couple of options.
If your hound is lippy on the leash when you stop wait until your hound stops, just stand there while he pulls, shuffles around, tries to shove his head in a bush (you get the idea) and as soon as he pauses with all four paws on the ground say "stop", treat, "let's go". Calmness and patience are the best training tools I have found yet.
Continue with the above until you stop and your hound is automatically stopping when you do. Once this is consistent you can move on and hounds which are well behaved on the leash it won't take long at all. You can do random 'stops' on your walk too, not just at roads or gates. If my hounds are getting a bit lippy on the leash I throw in a couple of 'stops' to get their focus on me, rather than the tree or bush that smells amazing, and it works a treat.
To move on from here start saying 'stop' as you stop, treat/praise as your hound stops. Then 'lets go' and carry on.
Next month we will move on from this point - Happy Training!