How to say "First" in Japanese

When translating "first" into Japanese, you must choose carefully between 最初 and 上旬. In Japanese, 最初 (さいしょ (saisho)) is typically associated with "first, beginning" (Syllabus Level: N4) and represents Refers to the initial part or moment of something. Contrasts with 最後. On the other hand, 上旬 (じょうじゅん (jōjun)) maps to "first third of a month, early part of a month (approx. 1st-10th)" (Syllabus Level: N3) and represents Refers to the approximate first 10 days of a month. Often used with a month name, e.g., 10月上旬. A literal translation of "first" can often sound unnatural to native Japanese speakers if mixed up!