All refers to three or more items. Examples are given below:

I will buy all three shirts.
I will buy both shirts. (NOT I will buy all two shirts.)

All and all of

Before a noun with a determiner (articles, possessives or demonstratives) all and all of are both possible.

I have invited all my friends. OR I have invited all of my friends.
All my friends have been invited. OR All of my friends have been invited.

Before a noun with no determiner, we use all without of.

All children need love. (NOT All of children need love.)

Before a personal pronoun we use all of. Note that we use object form of the personal pronouns after all of.

All of us like reading. (NOT All of we like reading.)
I have invited all of them. (NOT I have invited all of they.)

All can be put after personal pronouns used as objects.

She has sent her love to you all. (= She has sent her love to all of you.)
Mary has invited them all. (= Mary has invited all of them.)

All is used before uncountable and plural nouns.

All the water
All my children
All the milk
All the cake
All my friends

All with nouns

All can also be used before some singular countable nouns like week, family and way

All my family live in different parts of India.
He ran all the way to the railway station.

We do not normally use all + noun as the subject of a negative sentence. Instead we use not all + noun + affirmative verb.

Not all birds can sing. (More natural than All birds cannot sing.)
Not all Americans like hamburgers. (More natural than All Americans do not like Hamburgers.)