Star

A Star is an item in Child of Eden. It is obtained when completing an Archive.

Obtaining
Like I said, you can get Stars when you complete an Archive. The higher your score, the more Stars you will obtain.

Use
When you have enough stars, an Archive will be unlocked. If you can get more and more Stars, until you will eventually unlock the Journey Archive. Unlocking the Hope Archive does not require Stars, and instead requires you to beat the Journey  Archive once.

Even if you unlock more Archives, you can keep getting Stars until you get 999 Stars.