Your patron has given you a spell to summon a pair of spectral arms that are attached to the shoulders. They can be used as if they were your regular arms. Whenever you would use your strength Modifier, use your Charisma modifier instead.
At level 5, you can use your Action to teleport your arms off your body somewhere within 60 feet of you. But you cannot cast spells that need a somatic component. (items in your hands at the time of teleportation at teleported with the arms)
At level 11, it now costs a Bonus Action instead of costing an Action. You can cast Eldrich Blast from your arms when they are away from your body.
At level 17, you can cast any of your spells with your arms while detached from your body as if your arms were the source of the spell.
If someone casts dispel magic on your arms, instead of beating the regular requirements to dispel them, they must instead beat 10+ your spell-casting modifier.
* - (Pair of gloves)