We all know that Odoo community is a completely open-source ERP. Why should we prefer Odoo as our business management software? There are multiple plus points for choosing Odoo and one of the major points is Odoo is open-source software.
Actually, Odoo is a generic product that contains all the basic workflows that needed for almost all business areas like Trading, Shopping sectors, Restaurants, points of sales, Supermarkets, etc. But the nature of each business may vary. Then how do we make Odoo suitable to our business need? The answer is, we have to customize it according to our needs.
In general, there are two ways to customize Odoo ERP.
1) We can use Custom modules
2) We can edit via Front End.
Odoo App store is a one-stop destination for most of your customization requirements. You can find thousands of customized apps and Plugins there. https://apps.odoo.com/apps/modules

We can avail of almost 13000+ apps in the store. And Day by day the number is increasing. More and more apps and plugins are contributed by the Odoo community members. Odoo community is one of the highly-active open ERP community in the world.
You can search and find the best app that suits your business and fulfill your requirements.
At the top, we can see Categories, Free or Paid, versions. When you find a module that is perfect for your business then first check the versions.
The version of your Odoo ERP and Apps version must be the same. If your required app is on the Paid list, do the search again in the free category, it is highly probable that you may find a free variety of the same app.
Finally, if you found an app, then just download it by clicking the download button.
Once you download the app you will get the a.ZIP file,
Then how do you attach this app to your Odoo ERP?
Follow the below steps to Install Custom Modules in Odoo
You have to extract it first. Then you will get a folder containing __init__.py, __openerp__.py or __manifest__.py and other files.
1) Just copy the files and paste them into the folder (add-ons) of Odoo.

You may create a custom add-on folder here. Use the code to create one.
sudo mkdir /../../odoo/<custom_addons>
sudo chown -R odoo:odoo /../../odoo/<custom_addons>
Now you have to add the ‘custom_addons’ path in the ‘config’ file.
sudo nano /etc/odoo.conf (provide the exact path of the config file)
[options]
…………………….
…………………….
addons_path = /../../odoo/addons, /../../odoo/<custom_addons>
Edit the ‘addons_path’ and add your custom add-on paths.
Now you can paste your new app into this ‘custom_addons’ folder.
sudo scp -r <custom module>// root@<ip_address>:/../../odoo/<custom_addons>/
2) Once you finished the process restart the server to configure the file.
sudo service odoo-server restart
3) Now go to your Odoo home page
<ip address>:8069/web
4) Activate the developer mode.
To Activate Developer Mode
In Odoo V8 and V9 click on the right top Administration menu.
5) Click on About Odoo
6) Click on activate the developer mode.
In Odoo V10 and V11 Go to Settings
7) Activate the developer mode.
After that, update the module list by clicking the Update button
To update-modules
In Odoo V8
We can see this option in settings main
In Odoo V9, V10, and V11
This option is available In ‘apps’ Menu
Now your module is ready to install. Go to the apps and search your module, avoid the “apps” filter from the search bar.
Please note one important point, some custom modules may cause crash the DB or make some conflicts and show errors. So before installing the new module just take a backup file.
After the backup of the database search your custom module name and install it. And test it.
It is important to consider translations when we perform customizations in Odoo. In this blog let us see how to add the translation for the custom module and also the implicit and explicit exports in Odoo 13. Refer the blog on How to Add Translation to Custom Module in Odoo 13