Too and So

 
So, such, too
Examples: 

She was too reliable to lie.
Too + adjective + infinitive
She was such nice person that all her friends called her a peach.
 SUCH + adjective + noun  + that clause
It was so expensive that anybody was surprised.
  So + adjective + that clause

 

We use also SO with many, much:

There were so many books that we had read.

 SO + MANY, MUCH + noun +that clause.




Too / either   so am I / neither do I
Examples:

I am happy - My friend is too. So is my friend.
I enjoyed the trip - My friend did too. So did my friend. So did we!
She can't stand this man. I can't speak to him either. Neither can I.
They don't understand anything! I don't either! Neither do I!

 

We use too and either at the end of the sentence.
We use too after a positive verb
We use either after a negative verb
So am I = I am too. Neither am I = I am not either.

 
So ... (the result of something)
Because ... (the reason of something)