Parashas Vayikra · Aliyah 1 · Passuk 4
Chabad.org — English translation + Rashi
Torah Temima points to Yoma 36a (verified; how semicha is performed).
E-Daf.com — Tsurras Hadaf (size=3)
HebrewBooks / Shas PDF of the daf
English: Our Rabbis taught: How does one lean? The animal stands in the north facing west, and the one who leans stands in the east facing west, and places both hands between the two horns of the animal, provided that nothing intervenes between him and the animal. And he confesses: on a chatas, the sin of a chatas; on an asham, the sin of an asham; on an olah, the sin of a positive commandment and of a negative commandment that is remedied by a positive one.
Custom (procedural detail derived from the obligation of semicha) — the baraisa fills in the practical performance of the leaning commanded by the passuk.
The physical stance, placement of both hands, absence of a barrier, and the content of the confession that accompany semicha on the various categories of offering.