There's plenty of information out there on how to set up the PATH variable for your local shell for OSX - it uses the same method as people are used to on linux - settings in your shell config files.
But what if you want/need to set the paths at the system level? How is that handled?
Well - to start with - let's take a look in /etc/profile. Here you can see that it's calling /usr/libexec/path_helper.
More information on that can be found on the path_helper manpage
So - paths are being read first from /etc/paths then from any files in /etc/paths.d/
The files in the /etc/paths.d directory will be read in order based on filename.
So - you now have two methods - you can change the default ordering in /etc/paths (and if you wish add paths here) - I use this to move /usr/local/bin before /usr/bin and /bin - since I have my machomebrew files there and some of them overwrite the system files (for example a later version of git). Be aware that this means it's up to you not to install files there that are not backwards compatible - your system also uses a lot of files from /usr/bin and /bin :)
And if you want to install a set of paths for a given use/package/app then you can also choose to add that as a file under /etc/paths.d/
Note - you'll need to edit these files as the root user - sudo vi /etc/paths for example - and for that to work you'll either need to be an administrator of the machine or added to the /etc/sudoers file.
And finally - you'll need to start a new shell window before seeing the changes.