That is Amys bag
Amy's bag = la bolsa de Amy
This shop sells clothes
No apostrophes - 'clothes' is a plural noun
My friends phone is the latest model. (one friend)
friend's phone (el telefono de mi amigo)
Yesterday I bought some new shoes.
No apostrophe - 'shoes' is a plural noun
That is my parents house
my parents' house - la casa de mis padres
My friends have all got new phones
No apostrophes - 'friends' and 'phones' are plural nouns
Here is the principals office.
principal's office (oficina de la directora)
My friends phones are all new (lots of friends)
friends' phones ( los telefonos de mis amigos)
He is 6 years old
No apostrophe - 'years' is a plural noun
Those are the childrens shoes
children's - the shoes belong to the children