So and such are useful little words that can add color to your speech (that can make your speech more interesting). However, because they have similar meanings, it's easy to use them incorrectly.
So and such are both used to show extremes. They are similar to very (perhaps a little stronger).
So is used with adjectives and adverbs, often in exclamations:
He ran that marathon so quickly!
Oh my god! That was so fun!
Such is used with an article and an adjective before a noun:
He's got such an annoying voice.
You have to go to this restaurant they serve such delicious food.
Such can also be used with a judgement noun without an adjective. A judgement noun is a noun that has a positive or negative connotation:
That place is such a dump!
Be careful, though. These words are quite strong and can easily be over used. They can then become insincere (not truly meant). People who think that everything is 'so interesting'or 'so funny' can quickly become 'so boring.’
Unlike very, so and such can be used with that to show how the extreme nature of something has led to a certain result:
That woman is so beautiful that I'm going to cry!
I have such a terrible boss that I'm going to quit!
In these types of sentences, that can also be omitted (left out) without changing the meaning.
The Giants are so useless they'll never win another Superbowl.