When: This introduces a major category, which is the process of presenting an offering. This is followed by conditions introduced by "if" (1:3, 10, 14). Leviticus 1:2–6:7 uses this when/if pattern throughout all the major offerings it describes.
offering (Hebrew qorban; see study note on Mark 7:11) is a general term for all kinds of offerings and gifts, including those described in Leviticus 1–7.