what should be inside a / path code example

Example 1: add path to $PATH

PATH=$PATH:~/opt/bin
# or
PATH=~/opt/bin:$PATH

Example 2: add to path to PATH

FOR MAC:

 1º - Open Finder
 2º - Choose Go > Go to folder
 3º - Go to ~/Library/
 4º - Look for hidden files: Cmd + Shift + . (dot) 
 5º - Depending on the shell you use, the file can be .bash_profile, or .bashrc, or .zshrc, ...
 6º - Open that file in the text editor
 7º - Add the new path like: export PATH="$PATH:"User/new_path/..."
 8º - Test in your command line if it worked: echo $PATH