Nouns ending in -on are usually masculine.
Words ending in -tion, -sion, -son, or -aison follow different rules.
Is don masculine or feminine?
ledon
The rule behind it
91.9% of -on nouns are masculine
FrenchTextbook teaches rules like this, in a full beginner course.
162 lessons, 4,000+ exercises, and 6+ hours of audio.
Try the first lesson free