My Spanish isn't very good but to add on to what the girls said: 'so' is equivalent to the Spanish 'tan' If you want to say the dog is big and that is the end of the sentence then say "The dog is very big." "El perro esta muy grande." If you want to describe it more you can say: "The dog is so big that it is scary" "El perro esta tan grande que esta muy miedo." Sorry again if I only confuse you. Mi espanol no es bueno. lo siento

For intensifying (ex: the dog was so big / the dog was very big), they have the same meaning. We just use different words so that we aren't saying the same one all the time!

Most of the time, you can translate 'very' into Spanish as 'muy' (very big, very old) and translate 'so' into Spanish as 'tan' (so big, so old).