Hi Lince,

You can find an official tutorial (written by Odoo) here: https://www.odoo.com/documentation/9.0/howtos/backend.html
It explains the basic concepts pretty good. For further and more advanced things there are usually some tutorials on the internet too.

Yenthe

See the  simple example structure

 ◲ custom_module
 |___ ◲ models
 |    |___◫ __init__.py
 |    |___◫ custom_models.py
 |
 |___ ◲ views
 |    |___◫ custom_view.xml
 |
 |___ ◫ __init__.py
 |___ ◫ __openerp__.py

You can watch this on YouTube:  Create and install new custom module in odoo 10 

                        Note : __openerp__.py for odoo 9 and  __manifest__.py for odoo 10

Following are contents of each files.

custom_module/__init__.py

import models

custom_module/__openerp__.py

{ 'name': 'Custom Module', 
  'description': 'Description about your module', 
  'depends': ['base'], 
  'data': ['views/custom_view.xml'], 
}

custom_module/models/__init__.py

import custom_models

custom_module/models/custom_models.py

from odoo import models, fields, api 

class CustomModel(models.Model):
    _name = 'custom.model' 

    name = fields.Char(string='Name')

 <!--Create Top Menu-->
 <menuitem name="Top Menu" id="custom_top_menu"/> 

 <!--Create Sub Child Menu--> 
 <menuitem name="Sub Child Menu" id="custom_sub_menu" parent="custom_top_menu"/>

 <!--Tree view-->
 <record id="tree_custom_model" model="ir.ui.view">
   <field name="name">custom.model.tree</field> 
   <field name="model">custom.model</field> 
   <field name="arch" type="xml"> 
       <tree>
         <field name="name"/> 
      </tree> 
   </field> 
 </record> 
 <!--Form View--> 
 <record id="form_custom_model" model="ir.ui.view"> 
     <field name="name">custom.model.form</field>
     <field name="model">custom.model</field>
     <field name="arch" type="xml"> 
         <form>
            <sheet> 
               <group>
                  <group> 
                      <field name="name" required="1"/>
                   </group>
                   <group/>
               </group> 
             </sheet> 
          </form> 
       </field>
  </record> 
  <!--Define custom_action-->
 <record id="custom_action" model="ir.actions.act_window">
     <field name="name">Child Menu</field>
    <field name="res_model">custom.model</field> 
    <field name="view_type">form</field> 
    <field name="view_mode">tree,form</field> 
    <field name="help" type="html">
         <p class="oe_view_nocontent_create"> 
            Click here to create new item ! 
         </p>
    </field> 
  </record> 
  <!--Create child menu /Action menu--> 
  <menuitem name="Child Menu" id="custom_child_menu" parent="custom_sub_menu" 
                                                     action="custom_action"/>

I recomend download some module examples from gitHub and adapt the code.