Zend certified PHP/Magento developer

need help for installation of a extension WebP Optimized Images

I want install an extension:
Magento 2

Open Source (CE)

WebP Optimized Images

Component name:
jajuma/module-webpimages

Versions: 2.1.8

and tried to install with the installation sheet:

https://devdocs.magento.com/extensions/install/

I have the following questions:
When I do point 2 I will get the following message:

<oshopat01@vm30:/www$ bin/magento maintenance:enable
bash: agoshopat01@vm30:/www$: No such file or directory
<op.at$ bash: bin/magento: No such file or directory
bash: bash:: command not found

How can start point 4 to 6?
4. Update the composer.json file in your Magento project with the name and version of the extension.
5. Verify that the extension installed properly.
6. Enable and configure the extension.

  • Update your composer.json file:
    is it correct that I must insert in the file composer.json at “require”: the following:
    jajuma/module-webpimages:2.1.8

Here my composer.json file: https://www.dropbox.com/s/hsv8xs3wb4t49up/composer.json?dl=0

Must I start the command on the Server?
composer require jajuma/module-webpimages:2.1.8

Where must I insert the public und private Key ?

Which command must I use and activate instead bin/magento module:status J2t_Payplug.

For the registration and compiling I think I must use the same command linke in the guide?
bin/magento setup:upgrade
and
bin/magento setup:upgrade

Hope someone can help me there
kindly regards