This is the teachers room where all the teachers have their breaks.
teachers' room ( the room belongs to all the teachers) / teachers have their breaks - no apostrophes 'teachers' and 'breaks' are plural nouns
My friends phones are all new (lots of friends)
friends' phones ( the phones belong to my friends) / no apostrophe 'phones' is a plural noun
I dont like this cake
don't = do not
Im happy to see you.
I'm (= I am)
Ive got 3 sisters.
I've = I have / no apostrophe 'sisters' is a plural noun
Thats a good idea.
That's = that is
He is 6 years old
No apostrophe - 'years' is a plural noun
Were going on holiday tomorrow.
We're = we are
Heres the headteachers office.
Here's = here is / the headteacher's office (the office belongs to one headteacher)
Those are the childrens shoes.
children's - the shoes belong to the children
Thats Amys bag
That's = that is / Amy's bag = the bag belongs to Amy
Thats my parents house.
That's = that is / my parents' house - the house belongs to my parents
Lets go to the beach.
Let's = let us
She doesnt eat vegetables
doesn't = does not / 'no apostrophe - 'vegetables' is a pural noun
My friends phone is the latest model. (one friend)
friend's phone (the phone belongs to my friend)