Measure words 个, 本, 只
Chinese counts nouns with a measure word between the number and the noun.
Pattern: number + measure word + noun.
个 is the all-purpose one
one person
three apples
本 is for bound things like books
two books
this magazine
只 is for animals (and one of a pair)
one cat
two little birds
When unsure, 个 is understood almost everywhere, but the specific word sounds more natural.