My son has to identify stressed syllables with an accent mark and boldface for example forgot,because,daughter.can you help me??

2 answers

forgot'

because'

daugh'ter

You can check a dictionary (Dictionary.com) for the accents of other words.
Stressed syllables are just those that we pronounce a bit more loudly than the others. I'll indicate that with caps here:

SYL la bles (stress on first syllable)

for GOT (stress on second syllable)

be CAUSE

DAUGH ter

Make sense?