“So” is an adverb. It is use before an adjective or another adverb. The meaning of “So” is " very, to such a great degree”

Structure : SO + ADJECTIVE/ ADVERB
Ex - 1. The chicken was so delicious.
2. Those pictures are so beautiful.

Structure : SO + ADJECTIVE/ ADVERB + THAT + CLAUSE
" So … that" Structure is use to show cause and effect.
Ex - 1. Ram was so tired that he couldn’t finish the test on time.
2. Nina was so sleepy that she couldn’t concentrate on the lessons.