Numbers in Spanish
Cardinal numbers denote quantity, as opposed to order. To talk about order, you can use ordinal numbers.
Basic Cardinal Number Forms
Here are the numbers from 0 to 20, as well as the multiples of 10 from 10 to 100.
The numbers from 21 to 29 use a combination of veinti- and a number from 1-9 (with no space in between).
Note that veintidós, veintitrés, and veintiséis and have an accent on the last syllable.
Forming the numbers from 31 to 99 is a cinch. You just use a multiple of 10 plus the conjunction y and a number from 1 to 9. Here are some examples.
When to Use Cardinal Numbers
Besides being used to simply count, cardinal numbers are used in Spanish to tell the time and talk about dates and age.
To talk about dates, use the masculine singular definite article (el) and a cardinal number.
Cardinal Numbers as Adjectives
As mentioned before, cardinal numbers can be both nouns and adjectives. When a cardinal number is used as an adjective, it doesn't change to match the gender or number of the noun it modifies except in the cases of uno and cien.
Cien changes to ciento in numbers above 100 and changes according to the gender of the noun.