Nouns
Measure words
A number cannot go straight onto a noun. A measure word goes between them.
Number, measure word, noun, in that order, and the same after 这, this, and 那, that. English does it with some nouns: a cup of tea, a sheet of paper. Chinese does it with all of them. 个, gè, is the general measure word and is understood almost everywhere, so use it whenever you do not know the right one.
Examples
一个人yí gè rénone person个, the general one
两杯茶liǎng bēi chátwo cups of tea杯, for drinks
三本书sān běn shūthree books本, for books
这张票zhè zhāng piàothis ticket张, for flat things
Watch out
The mistake this causes
Leaving the measure word out, as in 一人 or 三书. Say 一个人 and 三本书.