We use either when we want one of 2 options, but it is not decided on which yet.
Do you want chicken or pizza?
Either is okay.
Means you don’t mind eating chicken or pizza. (Both is also possibility)
Do you want either chicken or pizza?
Either is okay.
This is the same but now, as either is in the question, both is not a possibility as you have restricted the options to 1.
If the 2 options are not clear, we can say the 2, after the word both – either A or B is
Either John or Sarah is working today
If the nouns of the 2 options are the same, we only need to say it once – Either of the (plural noun):
Either of the restaurants is fine.
Either of the cars are great
When using an object pronoun, we remove the ‘the’.
Either of them are fine.
Either of those will be great