Also / Too / Either

According to the Cambridge Dicionary of American English, these are the definitions for ALSO, TOO and EITHER.

ALSO - adverb - in addition
She´s a photographer and ALSO writes books.
ALSO can also mean similarly: That´s funny, I´m ALSO on a diet.

TOO (ALSO)adverb - (esp.at the end of a sentence) in addition; also
Bring your tennis racket, and your bathing suit, TOO.
TOO (MORE) - adverb - more than is needed or wanted; more than is suitable or enough
The sofa is TOO big for this room.
The apartment was nice but it was just TOO expensive.
TOO (VERY) - adverb - very, or completely
I´m not TOO sure I want to go out tonight.

EITHER(ALSO) - adverb - Used in negatives instead of also or too.
The restaurant has good food, and it´s not expensive EITHER.

ALSO
Use:
- before regular and irregular verbs in affirmative phrases.
- in affirmative phrases, after any auxiliary verb.
Example: She ALSO plays cards./ She is ALSO smart.

TOO
Use:
- at the end of affirmative phrases and before ny adjetive or adverb.
Example: They like samba, TOO./ Samuel is TOO smart.(here "too" is similar to "very")

EITHER
- also and too change to either in negative sentences.
Example: I want to come TOO. / I don´t want to come EITHER.
They ALSO want this book. / They don´t want this book EITHER.