Activation: first, commit an Evil act. The Roman Catholic Church’s definition of mortal sin will work, in this context: the act must be one of unquestioned and serious evil; the person committing the act must be fully aware that it is evil; and then he or she must commit the act anyway. This is admittedly subjective, and the usual instructions on how to perform the Sortitio Doloris are notoriously unhelpful on how to properly calibrate one’s Evil for this ritual. If it doesn’t work, then go out and commit another Evil act. No exceptions.
Assuming that a sufficiently dire act is committed, the performer of the ritual must then dedicate it to the ‘sponsors’ of the Sortitio Doloris in a somewhat complex and persnickety manner (one that roughly twenty percent of neophyte ritualists will fail to get right the first time). There are no second chances, by the way: flub the ritual, ‘spoil’ the Evil act that powers it. The only recourse is, again, to go out and commit another Evil act. No exceptions.
Assuming everything works: well, the ‘sponsors’ of the Sortitio Doloris will pick one entry as the winner, and reward that individual with riches, power, the death of his/her worst enemy, fame; the usual demonic gifts, in other words. This ritual won’t make somebody absolute ruler of the world, but it’s good for, say, shifting the results of a close election, or getting a coveted part in a major movie, or winning a crucial battle. Whoever loses will at least know that somebody won; and they will be able to recognize on sight someone who has won (whether in person or in recorded media). Otherwise, well, try again next time.
This nasty little Black Magical ritual can be found on the fringes of any organized and functional occult tradition that also has ‘demons’ (supernatural, malevolent entities that actively seek to promote the existence of Evil). Sortitio Doloris is nasty not because it’s inherently powerful; in fact, it’s barely magical at all. It’s nasty because it encourages horrible behavior.
While the ritual, technically, isn’t itself a damnation event, the buy-in for it does invariably require committing a sin that will send somebody to the local equivalent of Hell — and there’s no way to repent of it without also repudiating any of the rewards or benefits that came from it. Which is why ‘demons’ make the ritual available, of course. For every ‘winner,’ there are a host of ‘losers.’ It’d be cost-effective even if the ‘winners’ didn’t also go to Hell, in the end.
Which is, by the way, why the Sortitio Doloris ritual does only exist on the fringes. Any agent or agency of Good worth its salt ruthlessly exterminates all knowledge and/or organized promulgation of the ritual, up to and including physical immolation. The nicer groups give Sortitio Doloris ritualists an opportunity to repent and repudiate their sins first, but that’s not always guaranteed. Sometimes, that option is not even reasonable to expect. Evil is a lot less tolerable when it’s also being efficient.