Your patron gives you an amulet, a talisman that can aid the wearer when the need is great. When the wearer fails an ability check, attack roll or saving throw, they can add a d4 to the roll, potentially turning the roll into a success. This benefit can be used a number of times equal to your proficiency bonus, and all expended uses are restored when you finish a long rest.
If you lose the talisman, you can perform a 1-hour ceremony to receive a replacement from your patron. This ceremony can be performed during a short or long rest, and it destroys the previous amulet. The talisman turns to ash when you die.
In addition, you gain one bonus Eldritch Invocations which does not count against the number of invocations known. Otherwise it abides by the same rules and restrictions as normal and can be replaced when you gain a level in this class.
When you reach 10th level in this class, the d4s from your talisman are increased to d8s and you gain another bonus eldritch invocation, which does not count against your number of invocations known or the previous bonus invocation gained from the Pact of the Talisman feature. Otherwise it abides by the same rules and restrictions as normal and can be replaced when you gain a level in this class.