How To Add A Custom Admin Page To My Addon?

I want to have two separate pages for my addon. One with settings and one with an input field (this will send a message). I know how to build the settings page, but I need a way to add a custom page to my addon right under the settings page.

Why I need a separate page? Because this page will not have any settings in it. I will load a TPL file that will build a custom message based on the user input when it presses a custom made send button as well as other functionalities.

Have you read the developer documentation?

Basically every "mode" of a controller (addon) can have a corresponding template file that is loaded when the controller completes.

Most common template files that map to modes are:

+ manage

+ update

+ edit

+ import

+ etc

Hence a ?dispatch=my_addon.edit&id=123 would first execute app/addons/my_addon/controllers/backend/my_addon.php

It would act on the $mode, setting template variables, validating security, etc.

When my_addon.php returns, then design/backend/addons/my_addon/views/my_addon/edit.tpl would be loaded with the template variables set from my_addon.php.

For details, read the documentation.

Can you share the link to the docs that give more info about this? I know that my_addon.php is a controler but how it will run in the first place? I need to manualy add a button in the setting page that will redirect the user to that specific url?

Just google "cs-cart developer documentation"

I did and found it, but it says nothing clear about it... I read this but it says nothing about how to make the user go to that special link.

I explained in in #2 above. It is not a 'link', it is a page within the controller (addon) based on the 'mode' passed to the controller. Just go look at other addons that have multiple 'modes'.

Can you give me an example of such an addon? what I was able to find was only .post and .pre controllers

Suggest you review an addon like app/addons/reward_points and follow the logic through and then go to the design/backend/templates/addons/reward_points and again follow the logic based on the 'mode' being used in the controller. You will have pre/post controllers for other addons/controllers. The controller for the specific addon will be named 'your_addon.php' where 'your_addon' is the name of your addon.

If you want, you can also hire an experienced developer to do what you need.