Either... or is used to offer a choice between two possibilities.
Either Mike or Lisa will be there.
Either you leave me alone or I will call the police.
We should bring either coffee or tea.
You can either help us or go to your room.
Either of us could do it.
Either one of us could do it.
Either of you should know.
Either one of you should know.
Not... either... or denies both possibilities.
I don't think either Mike or Lisa will be there.
He doesn't speak either English or French.
Not... Either is used after a negative statement.
I don't speak French. You don't either.
He isn't ready to go. We aren't either.
