Parashas Vayikra · Aliyah 1 · Passuk 2
Chabad.org — English translation + Rashi
Torah Temima points to Toras Kohanim.
E-Daf / Tsurras Hadaf (size=3 where available)
PDF of the daf / source
English: “When he brings” – one might have thought it is obligatory; the wording teaches that it is voluntary.
Diyuk from the language “when / if he brings” — the conditional wording teaches that the offering is voluntary in its initiation.
Bringing an olah is optional (nedavah), not obligatory.