Hi,

We can install the oca module by clone the git repository in your server and add the directory to your `odoo.conf` file.

For better understanding you can follow the blog below.

And in the case of activating developer mode you can follow the steps below

General Settings -> Go to down using mouse scrollbar 
Where you will find the Developer Mode option with three different categories 
- Activate the developer mode - Mostly Used by the Administrators
- Activate the developer mode (with assets)  - Mostly used by the developers
- Activate the developer mode (with tests assets)  - Mostly used by the developers and testers.

Hope it helps