Strictly speaking "either" is an exclusive logical operator. Example: "You may choose EITHER x OR y." In everyday usage, "either" can be an adjective, pronoun, adverb (see fdmaxey's example) or conjunction. "Too" is an adverb, and it means "as well" or "excessively". Example: "It is too hot for me to work" (It is excessively hot for me to work) Example 2: "John is coming with us too" (John is coming with us as well) Both of them combined in an example: "Damn this weather! It is always either too hot or too cold!"

"Too" is used to include, "either" is used to exclude. "He's leaving tomorrow and I am going too." "He's not making the trip tomorrow. I'm not going either." "Either" has other uses, this time in a positive sense. "You can pick either the red or the blue car." It is used here to indicate a choice between two possibilities.

"too" can mean also or beside "I can clean and mop the floor too." "too" can mean excessive degree "Way too much food to eat." "too" can mean to be regrettable "This time Sally has gone too far." "too" sometimes can mean "so". "I didn't do it." "You did too."