When Emacs first visits an Org file, the global state is set to showeverything, i.e., all file content is visible6. This can be configured through the variable org-startup-folded, or on a per-file basis by adding one of the following lines anywhere in the buffer:

#+STARTUP: overview
#+STARTUP: content
#+STARTUP: showall
#+STARTUP: show2levels
#+STARTUP: show3levels
#+STARTUP: show4levels
#+STARTUP: show5levels
#+STARTUP: showeverything

Furthermore, any entries with a ‘VISIBILITY’ property (see Properties and Columns) get their visibility adapted accordingly. Allowed values for this property are ‘folded’, ‘children’, ‘content’, and ‘all’.