The exact details of this jutsu are unknown, but the general practice is that the user is able to seal away chakra into an object to be used for later. This technique is only seen to work when the seal is placed against something living like the flesh of a human or an animal. The simple truth is the chakra is compressed and stored within the seal until released for use at a later date. This seal can be opened and fed chakra but once the seal reaches a certain point, the next time that seal is tampered with, it will break and imbue the host with however much chakra had been placed within the seal. Once a seal is opened, the chakra is visibly emitted as a blue wing. As the user uses chakra, these wings dwindle in size until they are non-existent.
Unlike Tsunade's seal or the opening of the Eight Gates, the user is not increasing the flow of his or her own chakra or altering the body, but rather adding to the pool of chakra that can be commanded. This is not to say the technique does not drain the user, but fatigue and the loss of the sealed chakra are enough of a price to be paid for this technique. Also of note for this technique, there is a limit to how many of these seals can be placed upon the body; four at the most. To allow more than four seals of stored chakra to exist on the body will disrupt other seals storing chakra and render them ineffective.