Headlines define the structure of an outline tree. The headlines in Org start with one or more stars, on the left margin1. For example:
* Top level headline
** Second level
*** 3rd level
some text
*** 3rd level
more text
* Another top level headline
Some people find the many stars too noisy and would prefer an outline that has whitespace followed by a single star as headline starters. Clean view, describes a setup to realize this.
An empty
line after the end of a subtree is considered part of it and will
be hidden when the subtree is folded. However, if you leave at
least two empty lines, one empty line will remain visible after
folding the subtree, in order to structure the collapsed view.
See the variable org-cycle-separator-lines to modify
this behavior.
[1] See the variables
org-special-ctrl-a/e,
org-special-ctrl-k, and
org-ctrl-k-protect-subtree to configure special
behavior of C-a, C-e, and C-k
in headlines.