Hi Camila,
Drew has the right idea.
'Fair' is an adjective. 'Skin' is a noun. So you would say:
* She has fair skin.
Note that there is no hyphen " - " used here. They are two separate words.
You can also combine these two words to make a compound adjective:
* She is fair-skinned.
* Fair-skinned people need to take care when they go out in the sun
It is very common to make compound adjectives in this way. You take the adjective ('fair') , add a hyphen ( - ), then turn the noun ('skin') into a verb in the past participle form ( 'skinned' ).
Other examples are blue-eyed, short-haired, long-legged.
Why don't you try constructing a few words like this yourself?