How to use CLI commands

Hello,
I installed grav, got it to run.
However, I do not understand how or “from where” I can use the CLI.

After installing Apache and PHP, I found out that my “webroot” is /var/www/html/. My grav installation is at /var/www/html/grav/.

The first command in the GRAV documentation (https://learn.getgrav.org/cli-console/grav-cli) is:
$ bin/grav list
I tried to submit this command as follow:
user@computer /var/www/html/grav $ bin/grav list
/usr/bin/env: php: Datei oder Verzeichnis nicht gefunden
(My translation: File or directory not found)
I am not an experienced user in Apache, PHP stuff. I just wanted to concentrate on my website, blogs, etc., not having to use a huge relational database based CMS.

Can someboy explain me in a very basic way for newbies, how the commands of the CLI are intended to be submitted in the terminal?
Thanx in advance!

My system:
Linux Mint 17.3, 64 bit
Apache: 2.2(?)
PHP: PHP Version 5.5.9-1ubuntu4.16

I think the problem you have is that PHP is not found. Try typing php -v from the command line. You will probaby get a file not found error for that.

If so you need to locate your PHP installation and make sure that path to the CLI binary is in your user path.

Yes, you are right: calling php -v leads to the error you describe. The solution was however a little bit different as you propose: I had to install php5-cli. It seems to be necessary to run PHP scripts from the command line.
Now I can call the grav CLI. Thanx a lot for your answer, it gave me the appropriate impulse to search in the right direction.
Btw: it makes me very confident, that when I have a problem or questions, somebody will answer and help!

Glad you got your issue sorted!