Welcome to the forums.
how I can explain the difference?
Such
predeterminer, determiner
used before a noun or noun phrase to add emphasis
It was such a surprise.
predeterminer, determiner, pronoun
of a particular or similar type:
A company such as ours is known for its good treatment of its staff
noun
as such = in the true or exact meaning of the word or phrase:
There is no secretary as such, just a typist and receptionist.
So
•
adverb
1 to such a great extent.
2 extremely; very much.
3 to the same extent:
he isn’t so bad as you’d think
4 referring back to something previously mentioned.
5 similarly.
6 in the way described or demonstrated; thus.
•
conjunction
1 and for this reason; therefore.
2 (
so that) with the result or aim that.
3 and then.
4 introducing a question or concluding statement.
5 in the same way; correspondingly.