Jamieson, Fausset and Brown on Leviticus 1:3

3. a burnt sacrifice--so called from its being wholly consumed on the altar; no part of it was eaten either by the priests or the offerer. It was designed to propitiate the anger of God incurred by original sin, or by particular transgressions; and its entire combustion indicated the self-dedication of the offerer--his whole nature--his body and soul--as necessary to form a sacrifice acceptable to God (Ro 12:1; Php 1:20). This was the most ancient as well as the most conspicuous mode of sacrifice.

a male without blemish--No animal was allowed to be offered that had any deformity or defect. Among the Egyptians, a minute inspection was made by the priest; and the bullock having been declared perfect, a certificate to that effect being fastened to its horns with wax, was sealed with his ring, and no other might be substituted. A similar process of examining the condition of the beasts brought as offerings, seems to have been adopted by the priests in Israel (Joh 6:27).

at the door of the tabernacle--where stood the altar of burnt offering (Ex 40:6). Every other place was forbidden, under the highest penalty (Le 17:4).