How to install drush properly I am trying to install drush on my new computer and it's a mess
I'm on Mac Os High Sierra, with Mamp 5.3, PHP 7.2.14

I'm mainly interested in Drupal 7
On my previous computer, it was simple i just had to be on the htdocs folder and type : drush dl to download the latest Drupal 7 release

Now i had to install composer (v1.8.4) and then installed drush  using this command : composer require drush/drush:dev-master
I ended up with this version of drush (v9.7.0-dev)
When i type drush dl i get this message :  

dl has been deprecated. Please build your site using Composer. Add new projects with composer require drupal/[project-name]. Use https://www.drupal.org/project/composer_generate to build a composer.json which represents the enabled modules on your site.


I'm no advanced user (obviously), i just need drush to have persmission to execute basic commands to install a new drupal 7, install, enable, disable modules..                                  

Here's the result of $PATH

Mac:htdocs Mac$ $PATH
-bash: /Users/Mac/.composer/vendor/bin:/Applications/MAMP/bin/php/php7.2.14/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin: No such file or directory


Thanks
If you read the Drupal compatibility table in the docs, you'll see that the correct version for Drupal 7 is Drush 8. The installation instructions for Drush 8 are simple and clear, no Composer required - just download a phar file. 

PS! If you are planning on maintaining Drupal 8 sites (with Drush 9) too, I recommend getting Drush Launcher.