When we use C'

 In French, "C" is used as a contraction of the demonstrative pronoun "ce" followed by a form of the verb "être" (to be). It is commonly used in colloquial speech and informal writing to mean "c'est" (it is) or "ce sont" (these are / those are).

Here are some examples:

"C'est un chien." (It is a dog.)

"C'est une belle journée." (It is a beautiful day.)

"C'est important." (It is important.)

"Ce sont des livres." (These are books.)

"Ce sont mes amis." (These are my friends.)

In these examples, "C" stands for "Ce" (this/that) followed by "est" or "sont" depending on whether the subject is singular or plural. It's important to note that this usage is more informal than writing out "ce" and the appropriate form of "être" separately.