Either II

Either of

We use either of before a pronoun or a determiner (the, my, these...)

e.g. I don't like either of them.
e.g. I don't like either of my math teachers.

We can use either alone if a noun has already been mentioned.

e.g. Would you like coffee or tea? I don't mind. Either.

Please note that this is a sentence fragment. It is fine for conversational English, but should be avoided in written English.

Either I

We use either before a singular noun to mean "one or the other".

e.g. Come on Friday or Saturday. Either day is ok.

Sometimes either means each, especially in the expressions on either side and at either end.

e.g. There are flowers on either side of the door.