If your application server does not have a SSL certificate, you can shop online for one. You can get a paid version at https://www.thesslstore.nl/ or https://www.sslcertificaten.nl/ for instance or you can use the limited free version of https://letsencrypt.org/. Which one you use is up to you.
To check if your certificate is properly installed you can open your application server URL in your browser and check for a secure connection (most browsers will notify you when there is a problem with your certificate). Also you can use the online tool https://www.ssllabs.com/ssltest/ to do an elaborate scan of your certificate.
Note that servers should use TLS 1.2 or higher and route trafic only through port 443