Tamid, Chapter 6, Mishnah 3. This chapter follows the kohanim into the heichal to prepare and offer the morning service inside the sanctuary. Having dealt with the lighting of the menorah, the mishnah now arrives at the offering of the ketoret itself on the inner mizbe'ach, the mizbe'ach hazahav.
Two kohanim step into the heichal together. One is the kohen whose lot had fallen for the ketoret; the other is a companion or a kinsman whom he personally invited to come along and lend a hand. The pair now take their places within the sanctuary, alongside the mizbe'ach hazahav.
Handing over the spices
"Mi shezachah baketoret hayah notel et habazach mitoch hakaf," whoever had merited the ketoret would lift the small container out from within the ladle. Recall the arrangement described earlier: the spices were piled into a small container, and that container rode inside a larger ladle. The reason was purely practical. The small container was heaped to its rim, so whatever spilled over would drop into the ladle beneath it instead of being lost on the floor. He thus brought the two of them in together, removed the ladle's cover, and drew the spice container out.
"Venotno le'ohavo o likrovo," and he gives it to his friend or relative. He hands the ladle along with its lid to the helper who came in at his side, and the helper sets them down on the floor. Next the container of spices is passed over. The helper empties the ketoret out of it into the open palms of the kohen whose service this was, and places the emptied container on the floor as well.
"Nitpazer mimenu letocho," if any of the spices had spilled from the container into the ladle surrounding it, and catching such spillage was precisely the ladle's purpose, then "notno lo bechofnav," the helper would gather those spices too and pour them into his palms. Nothing was given up as lost. Even what had slipped away in transit was retrieved and delivered into his hands to be burned on the mizbe'ach.
The assistant has now finished his job. He bows down, takes the ladle and its cover with him, and leaves the heichal.
The instruction he receives
"Umelamdin oto," and they would teach him. Kohanim who had already performed this service in the past would coach the new kohen in how to do it properly. Why was he always a beginner? Because a kohen offered the ketoret only once in his lifetime. A fresh kohen was sought out every single time, since Hashem's beracha attached to the ketoret was wealth. The one who offered it became rich. So the privilege was deliberately rotated, spreading that beracha, quite literally, to as many kohanim as possible. Everybody got his turn, which meant the one performing it needed guidance from those with experience.
Here is what they told him: "Hevei zahir," be careful, "shema tatchil lefanecha," lest you start at the edge closest to you, "shelo tikaveh," so that you not be burned. Were he to set the spices onto the coals directly in front of himself, trouble would follow. Those coals are alight and throwing off heat, and should some spices fall, he would have to stretch his hand across the fire to retrieve them and would sear his hand and forearm. He was therefore told to begin at the far edge, toward the rear of the mizbe'ach. Whatever then fell would land on the near side, close to him, where he could pick it up without extending his hands over the flames.
"Hitchil meraded veyotze." He began spreading and leveling the ketoret out over the coals. When he was done, he bowed down, picked up the empty vessel, and left the heichal.
Waiting for the signal
"Lo hayah hamaktir maktir," the one burning the incense would not lay it on the mizbe'ach, "ad shehamemuneh omer lo," until the memuneh, the kohen appointed over the day's service, gave him the word: "Hakter." While the ketoret was being burned, no person was permitted to remain in the heichal, where the golden altar stood, nor in the ulam, the vestibule leading into it, nor in the stretch of courtyard lying between that vestibule and the altar outside. The memuneh would therefore first walk the entire area and confirm that not a soul was there. Only after he himself had withdrawn did he call out loudly that the time for the ketoret had arrived.
"Im hayah kohen gadol," should the kohen gadol be the one performing the ketoret that day, the summons was worded with added deference. The memuneh would not call out a bare "Hakter," burn it. His words were: "Ishi kohen gadol, hakter," my master, kohen gadol, offer the incense.
"Parshu ha'am," the people cleared away, emptying that stretch of ground which separates the entrance hall from the altar standing in the courtyard. "Vehiktir," he burned the spices upon the coals. "Vehishtachavah veyatza," he prostrated himself and departed, taking the emptied container out with him.