all
Refers to the entirety of a countable set; every individual person or thing in a group.
Alle meine Freunde kommen zu meiner Geburtstagsparty.
All my friends are coming to my birthday party.

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Refers to the entirety of a countable set; every individual person or thing in a group.
Alle meine Freunde kommen zu meiner Geburtstagsparty.
All my friends are coming to my birthday party.

The ending of `all-` depends on whether an article follows. Without an article, `all-` takes the article ending. If a definite article or possessive pronoun follows, `all` often remains undeclined.
Alle Kinder spielen im Garten.
All children are playing in the garden.
The form `alle` with an ending is used for countable plural nouns. The undeclined form `all` often stands before uncountable singular nouns, usually together with a possessive pronoun.
Alle Stühle in diesem Raum sind besetzt.
All the chairs in this room are occupied.
As a pronoun, the form `alles` (everything) is used and means 'every thing' or 'the entirety'. It is treated like a neuter singular noun and often stands alone as the subject or object.
Ist alles bereit für die Abreise?
Is everything ready for departure?
The phrase `vor allem` (above all / especially) is a fixed combination and means 'especially' or 'mainly'. It is used to particularly emphasize one part of a group or one aspect.
Ich esse gerne Obst, vor allem Äpfel und Bananen.
I like eating fruit, especially apples and bananas.
The meaning 'empty' or 'finished' is colloquial and especially common in southern and western Germany. This meaning is not used in standard language.
Kannst du neue Milch kaufen? Diese hier ist all.
Can you buy new milk? This one is all gone.
no / not any
'kein' and 'all' are clear opposites when it comes to quantity. 'kein' says that nothing or no one from a group is present or applies. 'all' says that the whole group is meant. So the difference is: zero versus the entire set. 'kein' often comes directly before a noun, for example 'kein Geld' (no money) or 'keine Zeit' (no time). 'all' is used for the whole of something, for example 'alle Kinder' (all children) or 'alles Essen' (all the food).

Alle Gäste haben nach dem Essen beim Aufräumen geholfen.
All the guests helped clean up after the meal.
Heute habe ich keine Zeit für einen langen Spaziergang.
Today I don't have time for a long walk.