It's for when you expose 2 potential options for something... For example: 1. What will you eat tonight? Either pasta or pizza, I haven't decided yet. 2. Someone can have a headache on either sides of the head or both sides. 3. This piece of information will either improve or hinder the process.

As Rilker has pointed out, 'either' can also mean 'also' in negative sentences: 'I don't understand this word. Do you?' 'No. I don't understand it either.' And here's another example, taken from a question which a member asked yesterday? 'Have you seen this film?' 'No. And I don't want to see it either.'

1.either I'll accompany you to your room, or I'll wait here 2.You can either drive your car to the grocery store, or ride your bike 3.The Ballroom has a bar adjoining for either sitting out or relaxing.