When. Recited over someone who is unwell — commonly with the hand placed on them, and often repeated three times. It is said by one person for another, in the second person throughout.
The words. Arqik is the verb of ruqyah: to recite over someone seeking relief. It appears twice, opening and closing the text, so the whole supplication sits inside a repeated frame — and both times it is bound to bismillah, never standing alone. The name is not decoration on the practice; the practice is only ever performed in it.
Min kulli shay'in yu'dhik — "from everything that harms you" — is deliberately unnamed. No diagnosis, no category. Then two specifics follow: nafs, a soul, and 'ayn hasid, the eye of an envier. And in the middle, the one sentence that is not addressed to the patient at all: Allahu yashfik, may Allah cure you. The verb of curing is never given to the reciter.
On the eye. Envy is treated here as something real that a person can be harmed by, and it is named plainly rather than hinted at. What the supplication does not do is instruct anyone to go looking for who the envier was.
What ruqyah is not. Nothing here involves objects, knots, numbers, written charms or payment. It is Arabic words said aloud over a person, and the text itself names Allah as the one who heals — which rules out the reciter being the source of anything.
In practice. Ruqyah with this text and with recitation of the Qur'an sits alongside medical treatment, not in place of it.