Installing Drupal

Hello I have installed drupal 8.9.0, and now i want to install the "commerce" module.
I read that I must to use "composer", for installing it and it should be native in this
version of Drupal.
 in the subfolder "drupal", on my web host, I can see the files "composer.json" and "composer.lock"
, but  when I try to run  the instruction "composer" via  the ssh connection,

I get  this messagge: "-bash: composer: command not found"

What am I missing?

Thanks in advance

I downloaded AppServ 9.3.0 for Windows 64 bit. I am running Windows 10 home, 64 bit. AppServ downloaded with no problem and installed,  Apache 2.4.41,  php 7.3.10 ,  MySql 8.0.17  and  php My admin db manager 4.9.1 .  I downloaded Drupal 8 and unzipped everything. When I enter Localhost, Drupal does not start or appear. Here is my directory structure; C:\\AppServ,  below directories Apache24, MySQL, php7,  www.   My Drupal directory is C:\\"drupal-8.9.1"   What is in the wrong place. What has to be started before Drupal will run.

My site is hosted on Hostgator.

They are planning to upgrade php version from current version 5.6 to 7.2+.

When i manually tried upgrading the php version to 7.4 using cpanel from multi php version, drupal stopped. I got following error message.

I trying istall drupal 9 on local server (xampp) , I face problem it appears on below:

1- PHP extension 

2- database support 

how can solve this problems 

I have been trying to move a drupal site (7.5.9) from an Ubuntu 14 sharedserver (Virtualmin) to an Ubuntu 18 vps server (Virtualmin). I have tried to use a full backup of the virtual server and restore it on the new server, but then I get:

The website encountered an unexpected error - and when I look in the watchdog table I see this error:

How we create a Hotel Booking website in Drupal?