After focusing and storing an amount of chakra over a period of time in the White Strength Seal on the user's forehead, the user releases the chakra with this technique, dispersing the seal and pumping the chakra back into the users body. Thanks to released chakra from the seal, Tsunade is able to use unique techniques. Firstly shown, she has used this stored chakra to perform the Creation Rebirth technique on herself and later on a separate occasion healed a vast amount of people through Katsuyu. During the Fourth Shinobi World War, Tsunade is also able to use the Strength of a Hundred Technique after releasing the seal.
In chapter 632, it was revealed that Tsunade has taught it to Sakura and that she [Sakura] had been charging it for three years. As of now, Sakura has yet to release it.
After using the chakra from the White Strength Seal for her techniques, if there is any leftover chakra, Tsunade may use it to re-form the seal as she did after her fight with Orochimaru.