Create Soul Gem

You grab a humanoid creature's soul, rip it out of their body, and stuff it into a jewel to create a Soul Gem. The requirements for casting the spell requires that the person has a soul to begin with (mostly they have to be of Humanoid origin) and they must be willing to have the spell be cast on them. If those two conditions are not met, then the spell fails.

The Gem then goes to the person of that soul. They still are alive and conscious while this spell is in effect, though there are some special conditions to it.

If the Soul Gem goes out of a 100 foot radius, the body falls prone and unconscious. It is rendered a corpse and is treated as such until the Soul Gem is returned to them. This also means that their corpse will rot if it is not returned to them. The soul in the Gem is still alive and can take over that remains of their corpse (with the exception of it being dust or ash) or with the help of a Clone spell or a similar spell, get a new body.

The Soul Gem is fragile, and so if it breaks, the soul dies with it. It is then treated as any dead character is treated as if it had freshly died, and thus, resurrection spells are usable.

If the Soul Gem is touched by someone who is not the owner of it, that owner makes a Constitution Saving Throw of your Spell DC. If it fails, they take 1d6 Psychic Damage. If they succeed, they take no damage.

A Soul Gem is permanent save for three exceptions:

The aforementioned destruction of the Soul Gem, which results in the trapped soul being able to be resurrected.

Casting Wish to negate the Soul Gem as if it never happened.

Casting a 9th-Level Dispel Magic spell while the Soul Gem is held closely to its owner, therefore returning the soul back to its owner.