Hi,
No app is required on Odoo. The synchronization will happen automatically as soon as the form is submitted. All needed is proper Odoo-Form mapping. Please make sure your Odoo instance supports API call. I have used a trial account created in https://www.odoo.com/ for testing purpose.
Steps:
1. Create your account in Odoo.com and make sure you have CRM module enabled. i.e, https://wassim.odoo.com
2. Install Ninja Form plugin on your WordPress website.
3. Create Contact Me form using Ninja Form and publish it on any Page / Post.
4. Install WP Odoo Form Integrator plugin on your WordPress website.
5. Go to WP Odoo Form Integrator Settings page and configure the server properties.
i.e, URL: https://wassim.odoo.com
Database: wassim
Username: YOUR_EMAIL_ADDRESS
Password: PASSWORD
6. Click Add New in Left Menu to open Add New Odoo-Form Mapping page.
7. Give any title
8. Select Ninja Forms in Form Type
9. Select Contact Me in Form
10. Select Contact [res.partner] in Odoo Model
13. Map name (Odoo Field) to Name (Form Field)
14. Map email (Odoo Field) to Email (Form Field)
15. Save Mapping
That is all. Now, you open the page/post where you have integrated the Ninja Form (Contact Me). Submit the form with any contact details and you can find the same created as Contact in Odoo server.
Hope this helps.
Thanks,
Siva