Pesachim, Chapter 5, Mishnah 6. The Mishnah continues its description of the order in which the Pesach offering was brought, dealing with the stages of slaughtering, receiving the blood, passing it along, and throwing it on the altar.
"Shachat Yisrael v'kibel haKohen":
The slaughtering was done by a Yisrael. As a general rule, the slaughtering of an offering is valid even when performed by someone who is not a kohen, and although the kohanim usually did it themselves, in the case of the Pesach offering - where the kohanim were extremely busy - they left the slaughtering to the Yisrael, and this is the practical halachah. Receiving the blood in a vessel, however, is specifically the task of the kohen, since from that point onward this is a service that is valid only when performed by a kohen.
"Notlo lachavero vachavero lachavero":
As we have already mentioned, a continuous line of kohanim stood here one after another: the one who received the blood hands it to his fellow, and his fellow to the one after him. And since they were passing the gold and silver vessels among themselves, the Mishnah adds: "Umekabel es hamalei umachazir es harekan" - the kohen first receives the full vessel from the fellow coming from the side of the slaughtered animal, and at that same moment hands him back the empty vessel, and so on down the entire line.
"Kohen hakarov etzel mizbe'ach zorko zerikah achas keneged hayesod":
The kohen in this line who was closest to the altar would throw the blood with a single throw. Unlike other offerings, the Pesach offering requires no more than one application of blood; but this application is done by throwing it onto the altar, and specifically at a spot directly opposite the yesod - the ledge that protrudes at the base of the altar.
This ledge did not surround the entire altar but only most of it, around three of its four corners:
At the southeastern corner there was no yesod.
According to various opinions, most of the southern side and the eastern side were also without a yesod.
The application of the blood is valid only at a place where there is a yesod, and this is what the Mishnah means when it says "he throws it with a single throw opposite the yesod."
The Gemara further explains that the kohen closest to the altar did not stand right up against it; rather, he would walk several steps from the place where he received the blood, and only then throw it. The reason is holachah - taking the blood and walking with it to the altar - which is one of the four primary services in the offering of a sacrifice. For this reason they left a gap that would allow for actual walking, for otherwise the line would have extended right up to the altar and the service of holachah would have been nullified.
In summary: In this Mishnah we learned the order of service for the Pesach offering - slaughtering by a Yisrael, receiving the blood by a kohen, passing the full and empty vessels along the line of kohanim, and a single throw opposite the yesod by the kohen closest to the altar, with care taken that it be at a place where there is a yesod and that the service of holachah be properly fulfilled.