1. We use 'either + a singular noun' to mean 'this one or that one' when we are talking about two things of the same kind (like two drinks or two t-shirts).
Either drink is fine. I like both kinds.
2. We could go to either restaurant.
Julie might buy either t-shirt.
3. We use 'neither + a singular noun'' to mean 'not this one and also not that one' when we are talking about two things of the same kind.
Neither drink is fine. John hates both of them.
Neither restaurant is good. Let's go somewhere else.
4. We use 'either of + plural noun' and 'neither of + plural noun' before a pronoun or a word like 'this' or 'the' or 'my'.
Either of my dresses is good. (= this dress is good and also that dress is good.)
Either of us can get the key.