Translation: “His linen tunic” — that it be according to his measure. “Upon his flesh” — that nothing interpose between it and his flesh. “And he shall take up the ashes” — he raked a full pan from the innermost consumed ashes and placed them on the east side of the ramp.
On the daf / in context: Terumas ha-deshen is an avodah requiring the four garments of an ordinary kohen. It is performed daily before the morning Tamid; the ashes are set beside the altar on the east of the ramp (Sifra; Yoma; Tamid).
Middah: Custom (halakhic detail derived by Chazal from the wording of the passuk).