The basic pattern
The pattern is number + measure word + noun. For “three books”, say 三本书 sān běn shū, not a direct translation of the English word order. The same pattern appears with 这 zhè (this), 那 nà (that), and 几 jǐ (how many).
The generic measure word 个 gè is widely used and is a reasonable rescue choice when you do not know a more specific classifier. It is not always the most natural choice, but it will usually be understood.
Five useful measure words
二 and 两 are not interchangeable everywhere
Use 二 èr when counting, reading a number, or naming an order: 二月 February and 第二 second. Use 两 liǎng before most measure words: 两本书 two books and 两杯茶 two cups of tea.
You will hear variation in fixed expressions and regional speech. For a learner, the number-plus-classifier pattern is the useful place to begin.
Practice with real objects
Walk around your room and name five objects with a number and measure word. Say the phrase aloud, then ask yourself 这是什么？ (What is this?) and answer with a complete noun phrase. This makes the classifier part of a useful sentence instead of an isolated grammar table.
When reading a new noun, record its common measure word beside it. Treat the pair as vocabulary: learn 一张票, not just 票. That habit prevents the classifier from disappearing when you speak.