Question

whats the difference in one cat's and two cats' as being possessive, basically, I am wondering what this ' at the end of words does.

Answer 1

Apostrophes are used to show possession, the one before the S is for singular possession - "one cat's". To show plural possession, make the noun plural first, then use the apostrophe "two cats'". Sometimes, although names which end in S or S sound are not required to have a second S, it is preferred (only personal names).

Answer 2

This way means something belongs to the cat:
The cat's food.

This way means something belongs to more than one cat:
The cats' food.