Numerals in English are mainly divided into cardinal numbers and ordinal numbers. The so-called cardinal number is mathematically understood as a number of equal size. Primitive words in English are used to describe the quantity of things.
In 1-20, except eleven, twelve, thirteen, five, eight, fourteen, six-ten, seven-ten and nine-ten are all composed of their single-digit forms followed by the suffix-ten.
Usage of cardinal words
Original words can be used as subject, object, attribute, predicative and appositive in sentences, which mainly indicate the number of things or people.
The two men happily opened the box. The two men opened the box happily. (as subject)
I need three altogether. I always need three. (as an object)
Four students are playing volleyball outside. Four students are playing volleyball outside. (as an attribute)
We are sixteen years old. We are 16 people. (as a predicative)
The three of them tried to finish the task before sunset. The three of them tried their best to finish the task before sunset. (appositive)