Well first of all you must be a runescape member. Once you have a membership complete the "Priest in Peril" quest to gain access to the Morytania/Mort Myre area.Once this step is complete simply go to the town Canifis [Kharyll in ancient magicks terms]. In Canifis there will be a clothing shop that sells red robes.
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you get ghostly robes after doing the quest desert treasure and then doing miniquests after then getting the robes as rewards
You can buy one from the bar in Falador or the bar in Burthrope
Great Question but to start you will need an amulet of ghostspeak (Restless Ghost) and ring of visibility (Desert Treasure)
You can find these in most of the pubs located in RuneScape, or for sale at the Grand Exchange. One is located in Falador, right next to the TelePort Station.
Go to varrock and go to the black wizard and you will find it. Or buy them at the Grand Exchange.