In the 18th century, Rowena created and used this spell to kill demons. When she decided to rebuild her power base, she started by recruiting girls from a demonic brothel and used the spell to kill Raul. This drew the attention of Crowley, Sam and Dean Winchester with the latter two identifying her as she was the only practitioner of it.
The website Sam was looking at identified the spell's use as "To Bind and Purge" which is what the spell's name translates to.
The spell requires the targeted demon to hold a hex bag full of unknown ingredients, with a sigil inscribed in it. Shortly afterwards, the demon will begin to violently cough itself up out of its vessel, and in its smoke form, will start to liquefy, and eventually die.
The spell is not able to kill the strongest demons - its effect on Crowley was relatively small. Though it pained him and made him cough blood mixed with his own demon essence, it wasn't able to kill him despite the fact that Crowley was exposed to the spell for several minutes. In fact, as soon as he escaped the devil's trap that was constraining him, Crowley was even able to burn the hex bag with his powers and disable the spell.