Can someone brake it down for me. Sometimes I mix them up. In witch situation exactly I have to use witch one and what is the difference?
This is the boys car. ("boys" can be also “boy is” and something more?)
This is boys car. (“boys” is used only when it is in plural?)
This is the boy car. (I think this is incorrect in any case, but still…?)
Maybe something more…
The boy is (this is called contraction, just as “I’m”, “don’t”, etc.).
The boy has (also contraction, but rather informal, not very common).
“The boys” is plural, no possessive.
"The boys’ " is plural possessive: “of the boys”.
So we can have:
The boy is stupid.
The boy’s stupid.
I am the boy’s mother.
The boys are stupid.
The boys’ bikes are still there. (The bikes of several boys.)
Then there is the compound noun, a noun made out of two nouns:
Tree leaf = the leaf of a tree.
Boy face = the face of a boy. Note that this is the same as “boy’s face”, which is in fact the better way to say it.
