Hola! I still haven't watched the first episode of season 10. I'm saving episodes so I can watch all the episodes at once during the next hiatus.
There are a lot of creatures in the TV Show. But we will only discuss ghosts and demons right now, since they are the creatures Sam and Dean deal with the most, with an exception of angels. Ghost are the first creatures introduced in the show. Ghosts are people who have died but they can't pass on to the next life because of unfinished business or brutal deaths. They become vengeful spirits and the longer a ghost stays on earth, the more violent it becomes.
A ghost can't pass a salt line, but they can use their powers and like blow the salt away. Ghost dissapear when they come in contact with iron, but they will reappear later.
There are a few ways to kill a ghost but the most common way is to dig up their bodies and salt and burn their bones. Sometimes a ghost is attached to an object, you will have to destroy the object then.
Demons are also recurring creatures. There are different levels of demons which result to some being immune to things that could kill other demons.
Lilith was the first demon created. Lilith was the first wife of Adam and she was a beautiful human soul. However as revenge on God Lucifer twisted her soul and made her the first demon.
Demons can't pass a salt line, but high-level demons can. Holy Water is also very affective against demons. It won't hurt their vessels (the person they are possesing) but it will hurt the demon itself.
Ruby's knife can also kill demons.
Angels can kill most demons and you could also use an angel blade. An Archangel can kill demons, since Lilith was very afraid of the archangel Raphael.
You can use a devilstrap. If a demon gets stuck in it, it won't be able to escape it unless the trap gets broken.
You can protect yourself with a pentagram-charm or an anti-possesion tattoo/symbool.
You can also salt and burn the bones of a demon, but this is very hard, since even demons have no memmories of their early life.
If you want to make the demon leave the person it's possesing you can use an exorcism:
Exorcism is a method to forcefully remove demons, Ghosts, and Angels from their Vessel commonly through Latin incantations.
It is probably the method with the best survival rate for possessed humans, even if some do not make it after the possession is lifted.
The best way to exorcise a demon is by making the demon get stuck in a devilstrap so it can't kill you. And then you will have to say the following
"Exorcizamus te, omnis immundus spiritus, omnis satanica potestas, omnis incursio infernalis adversarii, omnis legio, omnis congregatio et secta diabolica... Ergo, draco maledicte et omnis legio diabolica, adjuramus te ... cessa decipere humanas creaturas, eisque æternæ perditionìs venenum propinare... Vade, satana, inventor et magister omnis fallaciæ, hostis humanæ salutis... Humiliare sub potenti manu Dei; contremisce et effuge, invocato a nobis sancto et terribili nomine... quem inferi tremunt... Ab insidiis diaboli, libera nos, Domine. Ut Ecclesiam tuam secura tibi facias libertate servire, te rogamus, audi nos.'"