1. The Kohen Gadol must put the Ketores on the fire pan only inside the Kodesh ha'Kodashim.
2. The Beraisa describes what would happen after the Ketores was put on the fire pan.
3. Nadav and Avihu died because they ruled in a Halachic matter in front of Moshe and Aharon.
4. The Gemara gives examples of others who would back away instead of turning around and leaving.
5. One should take three steps back at the end of Shemoneh Esreh.
A BIT MORE
1. This is in contrast to the mistaken view of the Tzedukim that he must put the Ketores on the fire pan before he enters the Kodesh ha'Kodashim.
2. A pillar of smoke would go straight up and then mushroom downwards while spreading out, filling the entire Kodesh ha'Kodashim with smoke.
3. Despite the fact that they were correct, one is not allowed to issue a Halachic ruling in front of his teacher, as this is a sign of great disrespect.
4. When Kohanim would serve, Leviyim would sing, and Yisraelim would be in the Azarah representing Bnei Yisrael for the offering of the Korban Tamid, they would back away when they were finished.
5. One who does not do so is better off having not prayed at all.