Parashas Tzav is the second parsha in the Book of Vayikra.
 Overnight Burning
Hashem commanded Moshe to instruct Aharon and his sons regarding the burning of the remains of the Olah offering overnight. Sacrificial fats and animal parts that did not get consumed during the day are permitted be burnt by the fire of the altar all night until the morning. This teaching was given over as a 'command' which denotes urging to promptly and meticulously fulfill it both now and for future generations. This is especially true since it involved monetary loss of the daily Tomid offering.
 Burning of Invalid Sacrifices
If an invalid sacrifice was mistakenly brought up upon the Altar. If it had become unfit in the Beis Hamikdash the it was burned on the Altar and was not brought back down. However if it had already been previously unfit before it came into the Azara, like an animal that had relationships with humans, then it must be brought back down.
 Terumas HaDeshen
A kohen dons his linen Ketones robe which must be his exact size. He also puts on his linen Michnasayim pants with nothing separating it from his actual skin. He would then go up to the top of the Mezbeach and and would scatter the coals in all directions  and scoop out a full pan of ashes from the innermost part of the pile of burnt out sacrificial parts of the Olah that had been consumed by the fire of the Alter that had turned it into ashes. If he comes across any animal parts that had not yet been consumed into ashes, he must put them back onto the altar. He would take these ashes and place them down, next to the east side of the Altar ramp.