SO /  TOO is used for   “Positive Sentence”
For Example  :
->1. John is happy, so am I.
->2. Hadi speaks English well, Manik does too.
->3. Toni studied English yesterday, so did Rini.
->4. I have visited Bali, she has too.
->5. Dodik has finished SMP, I have too.
->6. I have visited Jakarta, so has she.
->7. Dodik can swim well, so did I.
->8. I went to Bali last month, so did Tina.
->9.  John is writing a letter, I am too.
->10. She was late yesterday, so was Doni.

EITHER / NEITHER is used for “Negative Sentence”.
For Example :

->1. John isn’t happy, neither am I.

->2. Hadi doesn’t speak Italian, Manik doesn’t either.

->3. Toni didn’t study yesterday,neither did Rini.

->4. I haven’t visited Bali, she hasn’t either.

->5. Dodik hasn’t finished SMP, I haven’t either.    –

>6. I haven’t visited Jakarta, neither has she.

->7. Dodik can’t swim well, neither did I.

->8. I didn’t go to Bali last month, neither did

->9.  John isn’t writing a letter, I am not either.

->10. She wasn’t late yesterday, neither was Doni.
For example :
->1. Either John or Tina speaks  English well.
->2. Neither John nor Tina speaks Indonesian.
->3. Both John and Tina speak English well.
->4. Both John and Tina don’t speak Indonesian.
->5. Either John or I speak English well.
->6. Either I or John speaks English well.
->7. Both restaurants are very good.
->8. Neither restaurant is expensive.
->9. We can go to either restaurant.
->10. I didn’t like either restaurant.
->11. Both of us were very tired.
->12. Neither of us is ( or are ) married.
->13. Neither of children wants (  or want ) to go to bed.

Both means
“One and the Other”
Either means
” any one of two”  
Neither means
“not one and not the other”