Hi, my dear friends! You all write many emotional blogs and comments here and often use these words, but you often use them incorrectly. So, I will give you some simple explanations so that you will not make such mistakes in the future.
SO is used before an adjective or an adverb:
The day is so nice! (an adjective).
He was listening to me so attentively! (an adverb).
SUCH is used before a noun or an adjective(s) + a noun. If a noun is singular and countable, there must be the article "a" before it.