'Everything' (todo) is a pronoun that can stand alone and be the subject or object of a sentence. For example:
Everything went well.
Everything is expensive.
I understood everything.
He has lost everything.
'All' (todo, todos, toda ,todas) is mostly used as an adjective, together with a noun.
I wrote to all my friends.
I stayed there all night.
He drank all the beer.
I've done all my homework