1. Explain it simply
否则 (fǒuzé) means 'otherwise' or 'or else'; it packs an implied 'if not' into one word.
Word order: requirement or condition + comma + 否则 + negative result.
The first clause says what should happen; 否则 then introduces what will go wrong if it doesn't.
否则 stands at the start of the second clause, right after the comma - not at the front of the sentence or at the end.
2. Show examples
你得快点，否则会迟到。
Nǐ děi kuài diǎn, fǒuzé huì chídào.
You have to hurry, or you'll be late.
否则 gives the consequence
你要多穿衣服，否则会感冒。
Nǐ yào duō chuān yīfu, fǒuzé huì gǎnmào.
You should wear more clothes, otherwise you'll catch a cold.
otherwise = or else
你要努力工作，否则会失业。
Nǐ yào nǔlì gōngzuò, fǒuzé huì shīyè.
You have to work hard, otherwise you'll lose your job.
the first clause states the requirement
3. Share a tip
否则 always heads the second clause; keep it right after the comma, as in ...，否则..., not at the end of the sentence.