They are used when speaking of different alternatives, and Either is used before the mention of any of the alternatives, and Or comes after.

Examples:

1. Either you go away (1st alternative), or I will call the police (second alternative).

2. You can either pay by cash (first alternative), or credit card (second alternative), or by cheque (third and final alternative).

I hope that is clear?

Also just to note that "either" can be used in other ways (without "or"); for example, you say "I can't stand hot weather". I feel the same, so I respond "I cannot either."

Either… or… connects two choices: I’ve saved some money to buy either a DVD player or an MP3 player. We use also either… or… to connect items which are the same grammatical type, e.g. words, phrases, clauses: We can either pre- or post-date the document. I don’t mind. (connecting prefixes) It’s either black or grey. I can’t remember. (connecting words) You can stay either with me or with Janet. (connecting phrases) Either I drive to the airport or I get a taxi. (connecting clauses)

“either _ or” = is used when there is a choice of two things that must be decided Generally, it is used for choices that must be made now or in the future. 1). In this example, “either - or” is used in the same sentence, and the choice will be made in the future: I will go to EITHER Peru OR Chile next month. In this example, “either - or” are used in two different, but related sentences, and the choice will be made now: 2) Question: Would you like eggs or bacon? Possible Answer: Either one. Possible Answer: Either is fine. “either - or” is only used in the past tense with the helping verb “to have”, in describing a choice made in the past: For his birthday, we HAD to choose between EITHER a party at home OR a party in a park, and we decided on a party in a park.

This is true, though many people will use "and/or" in less formal writing. For example, in an email, I might say "Mike and/or Steve will be attending the meeting."

yeah