• We use either before two or more persons or things, and use or to separate them.

EXAMPLE: You can borrow either one or two books for now.

• We use either when we have one of two or more choices.

EXAMPLE: Either she comes over to my place or I go over to hers as agreed.
EXAMPLE: It's either you send your old fridge for repair or you buy a new one.

• When there are two nouns in the singular and are joined by either... or, or neither... nor, they take a singular verb.

EXAMPLE: Neither the cat nor the dog is black in colour. (NOT 'are'.)
EXAMPLE: Either this frog or that toad is croaking. (NOT 'are')

• When the two subjects are in different persons, and the subjects are joined by 'or' or 'nor', the verb agrees with the subject nearest or next to it.