Yizkor, in Hebrew, means "Remember." It is not only the first word of the prayer, it also represents its overall theme. In this prayer, we implore G‑d to remember the souls of our relatives and friends that have passed on.
When we recite Yizkor, we renew and strengthen the connection between us and our loved one, bringing merit to the departed souls, elevating them in their celestial homes.
The main component of Yizkor is our private pledge to give charity following the holiday in honor of the deceased. By giving charity, we are performing a positive physical deed in this world, something that the departed can no longer do.
The soul gains additional merit if the memory of its good deeds spur their loved ones to improve their ways.