Can't make a technical explanation, but I hope this will help:
"So" doesn't have an automatic translation.
When you use "so" without a comparison (just to stress a situation), it's better to use "muy" in Spanish.
"Tan" is used when you're pondering.
Muy -> very, so.
Tan -> so (...that)
Estoy tan cansada, que quiero sentarme a llorar.
I'm so tired, that I want to sit down and cry.
Juan es tan guapo, que todos los hombres son feos junto a él.
Juan is so good looking, that every man is ugly beside him.
Esos niños son tan ruidosos, que los quiero estrangular.
Those children are so noisy, that I want to strangle them.
¡Te ves muy enfermo!
You look so sick!
¡Esto es muy raro!
This is so weird!
¡Esos niños son muy ruidosos!
Those children are so noisy!
No exageres, esto no es tan difícil (que no puedas entenderlo).
Don't exaggerate, this is not so hard (that you can't understand it).
Si al menos Juan no fuera tan maleducado (como es).
If only Juan weren't so impolite (as he is).
¡Tus plantas son tan bonitas (que me gustan mucho)!
Your plants are so pretty (that I like them so much)!
Parentheses here add some sentences that people can choose not to say, but that make the pondering complete.