After the two sons of Aaron died (in Parshah Shemini), G-d warns against anybody going into the special chamber of the Miskan called the Holy of Holies. Only Aaron himself may enter, once a year, on Yom Kippur, the holiest day of the year. Another thing done on Yom Kippur is that two goats are taken and a lottery is made. One goat is offered to G-d and the second one, to "azazel", is sent to the wilderness to atone for the sins of the Jews.
Other important warnings in the Parshah of Acharie: It is forbidden to bring a korban (sacrifice), anywhere but in the Holy Temple. It is forbidden to eat blood in any way (this is why all kosher meat is salted--to take out the blood, and why we check eggs for blood before using); and a discussion of those who we are forbidden to marry.