The system default
$PATH variable is set in the file
/etc/paths. That file has a one directory per line structure.
There are also multiple others files that can set or modify the path variable - user specific configuration files, and shell specific ones, that only apply if you use that specific shell.
I suggest not editing the system default file (
/etc/paths) as it would affect all users. To add directories to the path used in a Terminal session (and assuming that you use the default bash shell), generate a file named .bash_profile. With a text editor, create a line that adds the directories you want to the default path, e.g:
That will add the directories "bin" and "projects" in your home directory to the system path. You will need to either execute
source .bash_profile or restart your terminal session for that change to become effective.