Pfthb

I am new to the odoo and I developed a small custom module in odoo12. The problem is I am not able to see my custom module in the app switcher page after installing the module. (Below I gave the image link, where I am not able to see the module I have created after installing).

This is the link

The first step is you must define a menuitem, if you do not set a "parent" it will be a root menu and will therefore appear in the app drawer.

<menuitem
 id="model_menu_root"
 name="Module Menu"
 web_icon="module_name,static/description/icon.png"
 groups="base.group_user"
 sequence="6"
/>

You will probably want to have submenus to access your models, they will use this menu as their parent.

<menuitem name="Model Name" id="menu_1_list" parent="model_menu_root"
 action="action_window"/>

And the menu refers to the window action, which controls how your model is displayed.

<record model="ir.actions.act_window" id="action_window">
 <field name="name">Model Name</field>
 <field name="res_model">module_name.model_name</field>
 <field name="view_mode">tree,form</field>
</record>

You will need to define some security rules, otherwise the menu will not appear. These are controlled in the ir.model.access.csv file which must be declared in the __manifest__.py file. In previous versions skipping this step would be fine for testing purposes as the admin user would be able to see all models but this seems to have changed in v12 and you will need to define security rules before the menu becomes visible. Security rules are explained in the odoo developer docs https://www.odoo.com/documentation/12.0/reference/security.html

By the way, for a problem like this, usually the first place I would look would be the Odoo source code on GitHub. You can see how they have implemented the root menu and security rules on each of their modules and emulate it for your module.