It is only accessible after most completion of mournin'gs end part twoin the temple of light
You use rune essence/pure essence on a altar. (runecrafting)
Get rune essence and craft them at the air altar.
The altar locations are located by a "rune" icon on the world map. You can also find specific altar locations by Googling "Runescape Altar Map".
I believe that is the soul rune - a rune which you can't make, neither at a runecrafting altar nor with the new wicked hood. The only way to make it is at the Ourania altar, also known as the ZMI altar, which makes random runes, including the soul rune. It can also be bought from stores - and of course traded via the Grand Exchange.
You can make the at the water altar, buy them from a rune shop, or buy them from the Grand Exchange.
There is no special soul altar. From runescape.wikia.com: "The Ourania rune altar allows runecrafters to craft a random selection of runes, including the soul rune." So, if you go to the Ourania altar, you will craft random runes, including soul runes now and then.
They could be anywhere throughout RuneScape.
If you mean a talisman, a talisman is an item in RuneScape which, after completing the quest Rune Mysteries, allows you to create runes by having rune essence or pure essence in your inventory, mined from rune essence mines. Left click it to give you directions to the altar. Then, use the talisman on the altar, and click on the stone in the middle. Congratulations, you have made runes. Depending on which altar you went to, you will make runes of that kind.
You simply get some Rune Essence, and a tiara/talisman for the runes your creating ( depending on your level), then go to the appropriate altar and make runes.
You'll need rune essence or pure essence (depending on the rune). You'll also need a talisman or tiara of the corresponding type of rune you wish to make. Using the locate function on the talisman, you can find out where the altar is. Use the talisman on the altar to enter the altar. The move to the center of the new area and click the rock in the center. Once you know the location of the altar, a tiara (e.g. an air tiara, to craft air runes) is better, since it saves you one space in the inventory. You also need to have completed the quest "Rune Mysteries".
You will need a talisman of the opposite Element, Go to same altar as your tiara, and use the talisman there.
They are first at the cosmic rune altar, then the farm below falador, and the ogres or on a members server, east of castle wars.