Eclipse revolves about concept of perspectives. How many perspectives you have depends on how many plugins you have installed. A perspective is a visual container for a set of views and editors. A perspective is also like a page within a book. In a book there are many pages, in Eclipse you have many perspectives and, like a page within a book, only one perspective is visible at one time.
You can change current perspective by clicking on this button "Open perspective". In each perspective are views and editors in different parts of screen. You can open a new view in Window -> Show view.
You can save your changes you made to your perspective or even create your own perspectives. If you break it, you can reset chosen perspective to defaults.