There are two different kinds of word.
"was" = past of the verb "to be"
I was sad when my mother died.
"as" = can be a conjunction, an adverb or a preposition.
He came as quickly as he could. The first "as" is an adverb modifying "came"; the second "as" is a preposition, relating to the following verb clause "he could".
See here for a more extensive description:
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